I had a similar problem with the freshwater tanks on my 2012 28BHS. I believe my unit was towed up in winter on salted roads, just about every one of the self tapping bolts rusted and broke. They probably were over torqued at the factory. I replaced them all with bolts and nylock nuts. There's a lot of them!
We had the unit at a seasonal site, the corners of the freshwater tank started sagging under the trailer in hot weather, nearly 4", broke seal on the large joiner hose between the two tanks. I added extra angles to both tanks to support the corners more adequately.
I spent a lot of time under my unit the first year, very few screws holding the gray and black in place, propane line hanging by the copper lines, once again, broken bolts. Cleaned up the electrical, added hanger loops to hold the wiring up, repainted the frame as it was covered in rust. This was a new unit.
2012 Jayflight 28 BHS
2014 F150, 5.0 L, 3.55 axle