Dave,
Look under the forum heading "Coach in the making", thread is framing the outer walls.Those pictures were from a few months back. The box and bed were on the truck for a "clearance check" since I built them off the truck.
The floor is 2x4 11ga outer frame,floor joist are 2x3 11ga,walls and roof are 2x2 14 ga, roof outer frame 2x3 14ga. Skirts/toolboxes are 1.5 x 1.5 14ga. The box and bed have two 3x3 x .375 angle iron welded to the floor frame. The angle sits on top of mounts on the truck just like the factory sleepers are mounted . The box has six mounts and the bed has four. The mounts have rubber bushings that allow for frame twist and help isolate road vibrations. Most of the Toter's I looked at used a 1x4 on top of the truck frame rail and u-bolts like utility boxes are mounted. That also allows for frame twist. I just liked the way the factory mounted the sleeper. Just do not bolt it directly to the frame as it will shear the bolts or brake the mount. My neighbor has a factory built toter similar to what I am building.The 14ft box is bolted directly to the frame. At least twice a year he brings it over to replace the sheared bolts or reweld the mounts. The company that built it is no longer exists. I'll try to get a picture of the mounts posted.
Michael