We got our Montana High Country (41 feet long) last September and it seems that almost everything in the 5er broke at one point in time or another. Not dishes and stuff, but things like door frames, the underskirting popped out, and the rear closest (along the back) shelf holding the cloths bar collapsed. Not to mention some other things that literally "broke".
I'm using the trailer exactly as it came from the factor, except for the tires. We did change them after a blow-out (yea, it finally happened to me). But the tires themselves did not make any difference in the rear bounce or anything. No noticeable difference anyway.
I have since repaired and fixed stuff myself. I've re-inforced a lot of stuff, structurally and cosmetically. I will admit, the last few times out, nothing has fallen off or fallen apart. So, my carpentry work must be good.
With a trailer of this length, the rear is simply going to move up and down. The front may move only a couple inches up and down hitched to the tow vehicle, but the length on the other end of the fulcrum can cause the rear to bounce up and down a foot or more, and it can be very forceful.
No, I don't think you have issues with your suspension or tires or set-up. It's just pure physics.... you hit a bump and the shear distance magnifies the bounce very aggressively.
Consider the roads you are driving, consider those expansion joint bumps at bridges on interstates, consider all the chuck holes, cracks and rough places your tires hit. In your tow vehicle, you have lots of suspension and shocks and a soft seat you sit on. You don't feel the bumps. Your tires do... but you don't.
Your trailer does not have all that type of suspension, springs, and shock absorbers to cushion the compartment riding on those tires. Every hit of the tires is a hit inside that box, we call a trailer.
The best we can do is keep a screwdriver, extra screws, duct tape, and bubble gum around to keep fixing paneled wall, door hinges, toilet seats, sliding glass windows, wooden cabinets, and it's contents.
My suggestion ... well, there are many... Number 1, take different roads... Nah! That's not an option. Number 2 ... pack your breakables better. Expect the worst, be grateful when the worst doesn't happen.
We've had things break too, not just the actual trailer, but items made of glass and ceramics. I know, it stinks, but the solution is to simply pack them when traveling with a lot more cushion around them, since your trailer doesn't have springs and shocks like your tow vehicle does.
Good luck. I feel for you there. I really do. I understand.
