Building the camper's steel tube frame
My wife and I spent about four years plotting what features we wanted in our Unimog's expedition camper. For the first two years, we worked within the constraints of the 404 chassis. We eventually realized that the 404 just wouldn't be large enough for our requirements, so we decided to go with a chassis which would be able to carry our camper around without being overloaded.
The natural choice for us was the U1300L chassis - plentiful, inexpensive as surplus, decent surplus parts availability, and the ability to provide a decent, soft ride when loaded with our custom box. I began to work with my CAD software to design a shelter which would be strong, well-insulated, and comfortable.
Andie and I each had our priorities. Andie wanted warmth and a decent kitchen area. I wanted a good looking design that I could walk around in without crouching, and a REAL bed for sound sleep.
Our biggest decision came when we considered overall height. My Workshop only has 12' sidewalls with 10' tall doorways. From some rough scale-drawings, I'd clearly not able to drive into my shop for service if I built a box tall enough for me. We had four choices:
Build tall, and no longer be able to drive inside my shop
Build low, but fit inside the shop for service
Build a Hi-Lo system with a motor to raise and lower the roof
Build tall, but make the camper easily removable
The first two were quickly ruled out. I played with some jack designs for the third option, using acme screw thread and surplus windshield wiper motors, but decided against it due to complexity of the interior. I finally settled on the fourth option as the best compromise, since I could still get the chassis into the shop, the camper could now function autonomously when off of the chassis, and my Unimog chassis would be universal again and not dedicated to being a camper.
Here are simple street and curb side elevations from my CAD software. You'll notice available headroom is 6'3", there's a queen-sized bed, and Andie has an oven, fridge, and double sink. You can get details on those appliances on the Specifications WebPage. The main camper door will open to the rear, in two pieces. The lower piece folds down to become entry stairs, while the top hinges upward...
Once the plan was final, it was time to actually build it. First to come was the Torque Free Sub-Frame and once it was fabricated, I began by welding a level and square platform to angle iron which would nest in the sub-frame. The main structure of the floor is constructed of 2"x4"x1/8" rectangular tubing...
The overall shape of the side walls had to be constructed from 2"x2"x1/8" square tubing, and I did that on the concrete floor using chalk lines and some trig to keep everything perfectly square. The front of the camper is cut on a 45º angle to slightly reduce drag, while the back rakes upward at 51º to keep the Unimog's departure angle decent...
Once the side wall outlines were completely welded and ground, I raised them into position and welded them to the floor cross-braces...
With the sides installed, I could then begin to weld the vertical "studs," front and rear cross-pieces, roof, and window openings. Things are coming along nicely here, and Andie's beginning to see a real camper on its way...
I needed to removed the camper before finishing the roof, since my overhead door was in the way. In the photo below, I've removed the box using Rieco 2000# camper jacks and have finished most framework. All window and roof vent openings are installed, and I'm only lacking my rear door and rough openings for the side storage and mechanical compartments...