Convert a Truck Box as an Enclosed Trailer?

Here’s my idea: I can get a 26' aluminum truck box, the kind you see on big box trucks (not a semi dry van) with a rollup rear door and a plywood floor that has already proven itself with cars driven in and stored in it. I would like to mount it on an old 24' travel trailer frame that I stripped down. I would replace the springs with heavier new springs. An undesirable alternative would be to mount the box on my open car trailer which has 10,000 pound running gear.

I am moving my shop 1200 miles to my new house and shop, and of course I have several project vehicles such as a ‘50 Buick fastback and a clapped out ‘57 Chevy convertible. What I’m hoping to do is roll one car into the front of the trailer, then fill the back of the trailer with furniture and other lightweight stuff, trying to keep the total weight of trailer and cargo well under 10,000 pounds. Two trips and most of my stuff is moved.

Questions: would I run into some unforeseen engineering problem doing this? Towing this with my one ton dually, would I have to stop at truck scales in California, Oregon or Washington? Thanks for the advice. Tom

 

The problem I see is that travel trailer under carriages are usually not that stout. They were never designed to have a car in them. Although the springs, when upgraded would handle it, I don't think the rest of the chassis is up to the task.

The other point is that your 10,000 GVW of your car trailer would be perfect, except that your box would be included in the load portion of the GVW and could easily put you over loaded. If you can manage it, I would haul the cars on the open trailer, and then put the box on the trailer and load all the lightweight stuff at once. With the box hanging over the back of your trailer quite a bit, it would not take long to lose any tongue weight you have, and it is no fun driving a dually with no tongue weight...I had a trailer that actually was throwing my dualie rear back and forth once when I lost tongue weight, and it was pretty scary...finished the trip at a very slow speed, and ended up unloading and reloading in the dark...

 

And, if you are not running commercial tags, you should not have to weigh...but if you look overloaded or unsafe, you may be stopped and forced to get weighed. Depending on your etiquette and the officer's attitude.

 

depends on the axles, most travel trailer axles were rated 3500lb each

no stops needed at the scales

Welcome to the PNW

 

This is a 24 Foot FRP box mounted on a flat bed trailer.
The trailer was a heavy one and with the box weighs 5600lbs empty.

I placed the tourtion bar axels through the frame to get it lower, with wheel wells inside 8' high

The mack cab shell was an after thought to fill out the space in the front of the trailer. Plenty of storage there.

A box usually has a 4" channel or "H" beam that runs the full length spaced 34" apart. If you cut out a space in your camper cross members, you can weld them in place. You than can weld the box cross members to the trailer main frame. Should be strong enough as the box will give a lot of strengh to the unit.

 

Thanks for the advice. I too have learned the hard way about adequate tongue weight.

The walls and roof of the box are aluminum but the framework under the floor is steel with stringers about every 12 inches, and I'm hoping that by tying it into the frame rails of the trailer, there would be adequate strength.

Is there a way to look at or measure the travel trailer axles and determine their rating?

Regarding commercial tags, the trailer would be tagged private but trucks capable of hauling cargo in California all have to have truck plates, even pickups. Would that be considered a commercial plate?

 

Roger, thanks for the photos, I really like that front end.

Regarding cutting and welding frame members, my plan has been to leave the trailer frame alone as much as possible and cut into the frame of the box only as much as necessary to get them to mate as close as I can. In your third photo are the galvanized-looking parts your box and the rusty black parts your trailer frame?
Thanks, Tom

 

Tom, The black rusty parts are the axel and the frame rails.

The aluminum is the slide out ramp to drive the car up into the box.

I would strongly advise that you cut out a square space in your cross members and fit the main rails of the box into them and then fill in the cut areas and weld to the rails to restore the strength.

This will put the box cross members flat on the side main rails of the trailer and lower the whole box 4".

You may have to cut out the floor and instal wheel wells inside. These could be made out of 'stringer channel" . It is a very light weight channel iron used in steel staircases.

The box will supply a lot of strength to the trailer, probably more that the frame does..

(The box is strong enough to support its own weight, if sitting on the ground supported only by balancing it on a 4x4 beam in the center.)

 

Roger, thanks for the further explanation, makes a lot of sense.

I just went out and measured the frame and the main frame rails are 4" X 1.5" with 1/8" thickness, outside corners are square and inside corners are rounded. Not terribly strong, so your statement about the box adding a lot of strength to the trailer is encouraging.

I'm thinking about moving the axles back quite a ways to get more tongue weight, then adding a new rear section to the frame.

 

Cutting the crossmembers is a lot of extra work. I would weld the crossmembers to the top of the frame and add a handfull of gussets on each side for good measure.

 

This is also a 24' box that I cut down to 15'.

I only welded the spring mounts to 2" square tubing as shown. No trailer frame involved.

 

How is the tongue tied in Roger?

 

I know a guy who moved to Arizona from California. he bought a box truck, moved and then sold it. thought that might be something to think about.

 

Trailer toung is made out of 6" channel.

Ps, I had to show you what's hidding inside of this one.

 

Fun!

 

Roger, cool digger. The roll bars and large tube frame rails would date it in the late 50s?