U-Haul Box Truck Passthrough with an Accordion Boot

Creating a Passthrough in a U-Haul Box Truck

Here is a video by Techno Barbarian on YouTube showing how he created a passthrough while converting a 17′ U-Haul box truck into a mobile tiny home. I believe this is a pretty thorough process.

Understanding the Challenge

This type of U-Haul box truck has a plastic rear wall in the driver’s compartment. The wall includes ribs that help stabilize it, but those ribs pose a problem. They add extra length to the opening, which is an issue because the accordion boot requires both openings to be the exact same size. A workaround was needed to make sure the boot would fit properly.

Creating the Passthrough Openings

To begin the project, the placement and size of the opening had to be determined. The proposed opening was marked on the inside of the cab. Once it was outlined, a jigsaw was used to cut out the opening.

To make sure the front wall of the opening lined up with the cargo box, a drill was used. Holes were drilled along the edge of the cutout, which served as reference points. From inside the cargo box, those holes were then used to mark out and cut the matching opening.

Preparing the Openings

Once both openings were cut, they were inspected. A few issues needed to be addressed before installing the accordion boot.

Making a Flange for the Cargo Box

The first issue was the wall of the box truck. It has a plywood core, which made it too thick. The accordion boot requires a thin wall or flange—ideally between 1/16″ and 3/16″—so that the embedded spring clip can securely slide over it.

To fix this, aluminum flat bar was cut to fit around the perimeter of the opening. The aluminum protruded about 1/2″ into the opening. To secure it, holes were drilled at even intervals and the flange was attached with a combination of bolts, nuts, and liquid nails.

Modifying the Rear Cab Wall

The rear wall of the cab required extra work. First, the ribs increased the overall length of the opening. Second, the wall itself was too thick. To address this, the edge of the plastic was thinned out using an angle grinder. This created a lot of dust but allowed for a preliminary test-fit of the boot.

However, another issue remained: the half-round ribs running vertically along the wall. Even though the width and height of the cutout were the same as the cargo box opening, these bumps added 2–3″ of extra length to the perimeter.

Adding Flanges to the Rear Wall

To solve this, aluminum angle was used. It addressed both the thickness problem and covered the half-round ribs. This was an effective solution because it made the wall uniform and provided the proper flange surface.

The opening was cut to fit the aluminum angle, which was then secured with corner brackets. Caulking was applied to seal the gaps. With this, both openings were now exactly the same size.

Installing the Accordion Boot

Once all the adjustments were made, the accordion boot could finally be installed. Thanks to the preparation, this step went smoothly. Starting at one end, the boot was pressed onto the flange and worked around the opening until the ends met. The boot was overlapped a couple of inches to prevent any gap if the ends simply butted together.

My Thoughts on the Video

I found this video very instructional, and I believe it will help many others attempting a passthrough conversion. I appreciated how the builder tackled each challenge with practical solutions.

One concern I had was the 90-degree corners. Although he was able to force the boot around them, it is generally recommended to have a 1″ radius. In this case, it worked, but I would suggest either creating rounded fillers or using 45-degree corners to make the fit easier and more secure.

Another hindsight improvement might have been to create a flange for the cab wall rather than grinding the plastic. It would have been cleaner and less messy. Still, the overall approach was very effective, and the final result was impressive.