DIY Overland Trailer Build Part 3: Frame Design and Fabrication

I explained in the previous post in this series that I separated the design of my DIY overland trailer into various grouped elements. The first group was the trailer frame, suspension, and wheels. Here I’ll go through the design of the frame of how those all fit together, as well as the fabrication of the frame.

Topics

• Designing the Overland Trailer Frame

• Fabricating the Overland Trailer Frame

• Installing the Axeless Suspension

You can also watch the video that corresponds with this article:

Designing the Overland Trailer Frame

Because I plan to take the trailer into areas that are only accessible by relatively challenging off-road trails, I designed the trailer for large wheels and a lifted suspension. This would offer plenty of clearance when passed over rough terrain.

Initially, I planned to use the wheels and tires that I’d taken off my Jeep Rubicon when I installed a suspension lift. However, when I went to install the wheels, I discovered that they didn’t fit on the axleless suspension hubs I’d purchased, so I decided to buy new wheels and tires. I picked up two wheels and tires to match the new ones on my Jeep.

This added quite a bit of extra cost to the trailer build, but had the advantage of allowing me to run the same size tires on the trailer and my Jeep, which gives it more clearance and looks nice to boot.

To design the frame for my overland trailer, I took clues from how other people – both companies and hobbyists – built their trailer frames. I toyed with the idea of using aluminum for the frame to make it lighter, but I had no experience welding aluminum. Also, building a frame that was bolted together (a modern way to build an overland frame) seemed too expensive and complicated.

Materials

I decided to go with square raw steel tubing that was readily accessible, easy to work with, and a common material used in DIY trailer frames. For most of the structural frame members, I used 2-inch x 2-inch tubing with 3/16 wall thickness. For the trailer tongue, which connects the trailer to the vehicle, I used 2 x 2 tubing with a quarter-inch wall thickness for extra strength.

Mild steel is a type of carbon steel that contains low levels of carbon. It is also known as low-carbon steel or plain-carbon steel. The carbon content of mild steel is between 0.05–0.25 percent, making it relatively inexpensive compared to other steels. Mild steel is commonly used in construction and in manufacturing of vehicles and trailers, as it can be bent, welded, and cut easily.

Despite its name, mild steel can be quite strong, making it an ideal choice for a variety of applications. With proper care, mild steel can last for decades without needing to be replaced.

In addition to providing the strength needed for the trailer, the 2×2-inch tubing also fits the Timbren axle-less suspension and the Lock-n-Roll Hitch I planned to use for the trailer. I’ll go into more detail on the suspension and hitch later.

Length and Axle Placement

As for the overall structure of the trailer, I incorporated a number of rules of thumb that are often used to make sure trailers track well and that cargo weight is well distributed. I also had to deal with the fact that my trailer will live in my home garage when not in use, so it had to be short enough to fit.

Here are a couple of guidelines I used to determine the trailer’s length and the placement of the axle (in my case, the placement of the center of the wheels, since I used an axleless suspension):

60/40 Rule

The first rule of thumb is that the distance from the front of the tongue to the axle of a single-axle trailer should account for 60 percent of the total length of the trailer. The remaining 40 percent of the trailer’s total length should be behind the axle.

So if the trailer was 10 feet long, the distance from the front of the trailer to the axle would be 6 feet and the distance from the rear of the trailer to the axle would be 4 feet.

This is designed to help ensure that 60 percent of the cargo and trailer weight is in front of the axle. If the trailer is carrying too much weight behind the axle, it can become unstable.

Match Vehicle Wheelbase

The other rule of thumb is that the ideal wheelbase from the axle to the front of the tongue should be the same as your vehicle’s wheelbase or longer. This allows for the trailer to track well with the vehicle, which among other things makes it easier to back up. The wheelbase of my Jeep Wrangler Unlimited is 116” (9.6 feet), so ideally that would be the length from the front of my trailer tongue to the axle.

A quick disclaimer: I’m not an engineer and these are things I learned while perusing the internet. Take them with a grain of salt.

Because I had to keep my trailer under a certain length, I wasn’t able to follow the guidance above to the tee. The distance from the front of the trailer to the wheelbase was fairly close to 9.6 feet, but not quite that and the rear of the trailer had to be shorter than the 60/40 rule would call for, so the trailer is somewhat stubby in the back.

I’m seeing more overlanding trailers manufactured by commercial makers with the axle further back that the 60/40 rule would dictate. I’m guessing this is to keep the trailers shorter overall while still long enough to track well with tow vehicles.

Also, these are smaller tent trailers and teardrop trailers, so they may be light enough that overweighting the tongue is less of a concern. Maybe.

Another wrinkle is that someday I’ll probably drive something with a different wheelbase (a two-door Jeep Wrangler perhaps?!) but if all goes well, I’ll still have the overland trailer to take on adventures. So matching the wheelbase exactly isn’t necessary.

Frame Structure

As for the structure of the frame, I basically drew on designs I found online for overlanding and off-road trailers made of similar materials and for similar uses.

I made sure to place a cross brace around where I expected the axleless suspension components to the bolted on. The intention there was to provide more structural support in the area where the suspension and wheels would be mounted.

The frame also has a cross brace around where I’m planning to add a water tank (the middle brace in the photo above) to help support the extra weight. The frame looks sturdy to me and a lot like frames on other overland trailers I’ve seen, so the result is really a mix of crowd-sourcing and intuition. Guessing this isn’t how NASA builds rockets…I hope not anyway.

Fabricating the Overland Trailer Frame

Once I had my frame design completed, including accounting for the placement of the suspension and wheels, I started to fabricate the frame.

This required cutting the steel tubing, preparing it for welding, and welding the members together into a complete frame.

Working with mild steel tubing – and metalwork in general – requires some specialty tools. Here I’ll go through the various steps of fabricating the frame and the key tools required at each step.

Cutting Steel Tubing

To cut the tubing, I used a metal chop saw. If you are in the market for one, Evolution makes a terrific saw that’s well worth the money.

When building a trailer, you’ll end up cutting many, many pieces of metal. Get a good saw.

I used a variety of tools to measure and mark the metal for cuts – all of which were used in the other stages of the project. If you don’t have all of these, I recommend adding them to your tool collection as they are relatively inexpensive and make working with metal much easier.

Magnetic Tape Measure

These tape measures have magnetic discs attached to the hook that allow the hook to stay in place through magnetism while you measure. I have a Komelon MagGrip Pro and have no complaints.

Speed Square

Speed squares, also known as rafter squares, make measuring and marking 90-degree and 45-degree angles dead easy. Irwin makes a nice aluminum one in high-contrast blue and yellow that’s easy to read.

Silver Streak Marker

When you are working with metal, it’s helpful to have a Silver Streak Marker that writes with a highly visible line on metal. The line comes off fairly easily but typically holds during cutting and welding. I also like having a narrow black marker for cases where the silver isn’t visible (on shiny metal, for instance).

Angle Grinder

An angle grinder is an essential tool for metalworking. You can use the grinder with cutting wheels for cutting metal; with flap discs to grind and smooth the metal; and with stripping pads to remove the mill scale (see below).

It’s nice to have a cordless version, but I’d recommend getting one with a cord first, as you’ll use it so much that it’s difficult to keep batteries charged. Dewalt makes an affordable one design for use with 4.5-inch discs that’s a good option (pictured here).

Removing Mill Scale

Straight from the metal yard, mild steel has an outer coating called mill scale that must be removed before you can weld the tubing together. The mill scale is a pain.

I tried lots of different ways of removing it, from grinding it off to soaking the metal in vinegar (which works, but is difficult to do with long pieces of steel, and time-consuming).

The best way I’ve found to remove the mill scale is using Scotch Brite Clean and Strip XT Pro Discs with an angle grinder or polisher.

Made by 3M, these discs are amazingly good at removing mill scale, rust, and other gunk from the surface of the metal. I want to say I went threw four or five of them in the process of making my trailer. It still takes a lot of elbow grease to remove the mill scale, but the discs make it a lot easier.

After I cut the metal, I used the Scotch Brite discs on a polisher to clean the mill scale off. My polisher is one made by Milwaukee that I used to use to shape surfboards. They are hard to find and probably more expensive than necessary for this job. Dewalt makes a polisher that’s more affordable and will do the job.

As I noted in the previous section, you can also use an angle grinder for the same work, and the angle grinder can also be used with cutoff discs to cut metal. If you don’t have the budget for a polisher and an angle grinder, get an angle grinder. The nice corded Dewalt angle grinder mentioned above works with the 4.5-inch Scotch Brite discs.

It may feel a bit old school, but I recommend buying a corded angle grinder and/or polisher instead of a battery-powered one. Unless you have a lot of extra batteries, you’ll struggle to keep them charged.

One mistake I made was not completely removing the mill scale from the tubing before welding the frame together. I cleaned the areas of the frame tubing where I planned to weld it together and left the rest for later.

My thinking was that the metal would likely rust anyway since I’d be working on the trailer for a few months, which it did. But it turned out to be easier to remove light rust than mill scale, and getting to certain areas of the frame with the polisher was challenging after I’d welded it together.

After stripping off the mill scale, I cleaned the metal with acetone to remove any remaining residues and dirt. The stripping process kicks off dust and leaves behind some streaking that needs to be cleaned up before welding. Which brings me to another topic – safety. When working with power tools, it’s important to protect your body, both the outside and the inside. I typically wore long pants and shirts, thick socks, and close-toed shoes.

I learned the hard way that cotton or wool is better than synthetic materials when working with metal. The metal flakes that fly off when you are cutting, drilling, and grinding are often very hot and will melt right through synthetic fabrics (eg, nylon and polyester). It doesn’t feel good when this happens, nor when you happen to be wearing flip-flops, and a hot cast-off from drilling metal lands between your toes. Trust me.

Below is a list of personal protective gear (PPE) that I used when cutting, grinding and prepping the metal:

• Face shield and/or safety glasses

• Leather work gloves

• Safety earmuffs

• Respirator

It can be a pain wearing all this gear, but going to the hospital with a shard of metal in your skin or eye or damaging your lungs is a lot worse.

Welding the Frame

Once the pieces of frame tubing were cut to length and the mill scale was removed from the welding area, I laid the frame out on the floor of my garage. I used the speed square and welding magnets to get the frame members squared up and held in place. Then I tack-welded the frame together to hold it in place before fully welding the joints.

After I tacked the frame together on the garage floor, I used jack stands to alternately lift the different sides to fully weld the members together. Lifting the frame like this made it easier to run the bead on the seams. The positioning was more stable and comfortable, and I could choose whether to run the bead uphill or downhill (welder talk for moving the tip up vertically or down vertically).

I won’t get into the nitty-gritty of welding in general here, as it’s a complex subject and there are plenty of resources online. For reference, I was using a MIG welder plugged into the 240-volt plug in my house – the outlet our dryer is typically plugged into. I used .030 gauge welding wire for welding the frame.

If you are looking for a welder, the Reboot MIG Welder 210A and YESWELDER 205DS machines are very affordable multi-process welders that can perform MIG, LIFT TIG and stick welding. While I don’t own either of these (I have a Vulcan multiprocess welder from Harbor Freight), I’ve heard they are great machines for learning to MIG weld.

If you have the budget and are looking for a top-of-the-line welder that will last you many years, check out the Miller Multimatic 215 multiprocess welder (be prepared for sticker shock). This one’s on my wish list.

A word of caution here: don’t weld a trailer for highway use unless you are very confident in your welding skills. Check out your local off-road club to see if they can point you to classes or check out your local community college.

Once the frame was fully welded and the holes for the axleless suspension drilled (see more below on the suspension install), I still needed to remove the rest of the mill scale (the result of the error in judgment I mentioned above). It was a lot easier to remove the mill scale when the polisher or grinder was on top of the metal, since gravity helped hold it in place.

I ended up moving the frame into all sorts of different positions to accomplish this. My neighbors no doubt thought I’d lost my mind. Once I’d removed all the mill scale, I used acetone to clean up the frame and put a coat of primer on it to prevent rust during the build process.

In retrospect, this was a really smart move, as it took me over a year to finish the trailer, and the scrap metal that I stored in my garage all became covered in rust during that period.

Installing the Axeless Suspension

While many overlanding trailers have traditional axles, I opted to go with an axleless suspension from Timbren. From my research, the axleless suspension offered more clearance and looked as simple if not simpler than a traditional axle to install.

The Timbren axleless suspension is a kind of independent suspension for trailers. Each suspension comes with two components, each of which features heavy-duty outboard arms and long spindle arms that can accommodate larger off-road tires.

One of these suspension elements is mounted on each side of the trailer with large bolts that go through holes drilled in the trailer frame. The outboard arms drop 4 inches from the frame, which puts the center of the wheels lower to give the trailer more clearance. The arms absorb bumps in the road thanks to large rubber bushings that get squeezed when the arms compress into the frame mount.

I chose a Timbren axle-less suspension that was rated to 2,000 pounds, as I don’t plan for the trailer to exceed that weight. When the rooftop tent is deployed, we will use stabilizer jacks that will take some of the weight off the suspension (more on that later).

Truth be told, an axleless suspension may be overkill for many people. With larger tires, a traditional axle may offer plenty of clearance if you plan to stay on fairly mellow dirt roads and trails. Also, you may be able to find one cheaper than the Timbrens. For instance, it looks like you can piece together an axle and suspension from Compact Camping Concepts (Dinoot Trailers) for under $500.

I will say, however, that the Timbren suspension was very easy to install and does give the trailer a ton of clearance. To mount the suspension on the frame, you drill a few holes and then use large grade 8 hardware to attach it. There are some extra holes in a plate on the suspension components that can be used to bolt it to an additional plate welded onto the frame to provide more support.

Another tool that is clutch when working with metal is a step drill bit. These bits, which have different diameters of “steps” to cut holes, make drilling holes in metal go much, much faster. They are especially helpful for smaller holes but still struggle at larger diameters such as 1/2-inch holes. Still, they will get you started on large holes and you can then switch to a single-diameter bit to finish the hole off.

Another option is to use a 2 x 2-inch cross member that slots into brackets on both suspension pieces. This provides a single direct connection between the components that provide more support for them. While it does reduce the clearance slightly, I opted to include this cross-member for peace of mind.

You can see the cross member running between the suspension components in the image below. It’s bolted to them at either end.

Assembling and Connecting Timbren Hubs

After I had the base of the Timbren’s connected to the frame, I attached the outboard arms and spindle. Adjusting this connection is how you set the toe of the wheels – which came later. I also purchased hubs from Timbren, which are the connection between the outboard arms and spindle to the wheels.

I chose hubs with electric brakes, as I wanted the trailer to brake with my Jeep, particularly on technical trails and steep downhills. Later on, this required wiring the hubs to the 7-pin connecter for the Jeep, but more on that later. Mounting the hubs took a while, as you have to assemble the hubs, which includes packing the hub bearings with grease and pressing them into the hub.

Once I had the hubs mounted on the outboard arms, I attached the tires. For reference, if you are buying hubs for your trailer, you need to make sure they match the pattern of the wheel you’ll be using. The wheels I bought matched those on my Jeep, so they have a 5×5 hole pattern. Some car and trailer manufacturers use different patterns.

XO Trailer Jack

The last step in this phase of the trailer build was to attach the XO Trailer Jack to the front of the trailer so that it could stand on its own. These jacks are designed for trailers that will be taken into rugged conditions. They are super sturdy and come with a large wheel for rolling across rough ground.

Getting to this stage felt like a real accomplishment and the ability to move the base frame around was helpful. In the next post, I’ll go through the steps to make the cargo box on top of the frame. I’ll also share how I mounted the fenders, which turned out to be one of the more complicated engineering feats of the build.

All Overland Trailer Build Articles

• Step 1: Choosing a Trailer Style

• Step 2: Design Process

• Step 3: Frame Design and Fabrication

• Step 4: Cargo Box, Doors, and Fenders

• Step 5: Cladding, Trim, and Painting

• Step 6: Wiring Harness and Tail Lights