Frames and axels

+1. In the meantime you can import foreign manufactured  vehicles if they're over 25 years old without them meeting federal standards. Beware your state requirements though. The Japanese ones I'm looking at are very practically designed, fiberglass coach work,  high on quality and low on unnecessary frills. They also tend to be well maintained and have low odometer readings. Very robust 4wd diesel truck chassis, don't think bent frames and axles are a problem. But they won't win any races for sure. Don't know about importing towables. 

I have heard of the cracks on the outer and inner walls from several people. The cracks predominately happen over the door, in the top left corner. Although your case may be different, It's possible the cracking has nothing to do with the axle.  If you look at the crack, it might be apparent that it was caused by "upward" force. The culprit being the stabilizer jacks. The door opening in the rear leaves a very thin strip between the door, and the rear of the camper. The stabilizer is able to put quite a bit of force lifting the back end of the camper with (for lack of a better term) a "hinging" effect. The rear corner being supported only at the top of the door. I noticed that on mine, the rear passenger area was easy to actually lift that corner with minimal effort. There was plenty of support for downward force, but virtually none for upward force. 

It's the axle imposing stress on the frame at that point. Well understood effect of torsion axles. You can see a finite element analysis showing the high stress location here: