HF 4x4 Enclosed to 4x8 Utility Conversion Trailer Build - Adapt for Offroad


I am posting this build in expedition trailers, because I believe this concept may be useful to some people looking to build a dual purpose offroad trailer. Basically, it will be a small enclosed box trailer, that I can tow behind my prius. Ultra light. But, it can unfold from a box, to an open utility trailer big enough to haul plywood and 2x4's from the hardware store, or move a piece of furniture. I think there are people who may want an enclosed expedition trailer, but also want it to serve as their utility trailer for use around home.

I started with this:

I bought it on sale, and with the 25% off coupon at easter. So, it was like $165 with tax. I opted for the larger 12" wheels to be able to tow at highway speed better.

Here is the concept:

I am welding a 1/2x1/2" steel tube frame, then attaching aluminum panels. The aluminum are just road signs I got from a buddy in civil contracting. Trailer weighs 150lbs to start. Hope to not add more than maybe 150 lbs. I will add a sliding tounge, sleeved in the original tounge, that can extend when you are in 4x8 utility mode. Lid doubles as a ramp when in utility mode.


obtained all the road signs from my buddy. should work nicely. You could try to call the construction sign companies (the civil construction companies hire out the signage and flaggers etc I think) and buy their used signs for scrap value.

mocked up the new sliding tongue. I got a thick steel tube to slide into the original tow bar. It will telescope in and out, depending if I am in cargo box, or open utility mode.

Here it is in compact mode:

Here it is in extended mode:

Could not use the original bolt locations as they interfered with the sliding tube. So, I welded the bar in place:

For extra support under the deck, I just added some 2x4's.

Cut up one of the large 48x48" orange road work signs. This will be my deck.


I certainly like the idea of a multi-use trailer. Looking forward to seeing how this comes out. I would love to have something similar that even my Neon can tow coast to coast.


Mine is coming along pretty well. I have not been very good about taking pictures. Guess I'll just post a bunch of the finished trailer. I was watching that video again, it takes 2:45 to convert from box to utility. If I had to do all those steps it would drive me nuts. Hopefully mine turns out quicker. Mine will also convert to a flat bed trailer. The entire box assembly will be removeable in 20 seconds I think. I hope to find somewhere to weigh the finished trailer as well. I am guessing its going to weigh less than 500lbs.



Ok... fast forward. Its done. Turned out decent. Tows great on asphalt, but on the concrete highways it sure gets a bouncing. suspension is way too stiff with the trailer unloaded. Not sure there is much I can do about that.

Here it is all folded up in cargo box mode. Drawbar is slid in, keeping trailer close and in the slip stream of the prius for better gas mileage.

2" ball hitch. The t shaped thing is a support for the folded down front half of the trailer when its in utility mode. The red handle is a pull pin. You pull that and slide out the drawbar for utility mode.

Here it is unfolded into utility mode.

Roof of box, folds down into ramp for utility mode.

Back in cargo box mode. The ramp/roof opens for access to the box. Box is closed in with rubber seals all around to make it dry. So, I can hopefully haul luggage on a roadtrip or whatever.

Looking inside the box, at the fold down walls. These are the middle walls when you see it in utility mode.

When its in cargo box mode, everything is held together with adjustable draw latches. In utility mode, the walls and all connected together using pins.

Lastly, it can be used as a flatbed trailer. The entire box is attached to the deck and frame using 4 draw latches. Don't have a picture of that yet.


technically I don't think the prius is rated to tow anything. But people do it all the time, and I don't plan to put more than a few hundred pounds in there, which is not more than having 4 adult passengers in my car anyway.

I will try to make a video of it unfolding and put it on youtube.
Last edited: