[flybouy]

First welcome to the forum.

Whomever told you that Keystone "might cover that under warranty" was smoking something. Warranty coverage on a second owner 7 yr old trailer? In your dreams. That is a "hung rear wall", it is not laminated. They all "buckle" from day one. They are only secured around the perimeter, around the window, and where the ladder and lights are screwed in. So as the wall heats up the unsecured areas buckle when it expands. The older it gets the more it will deform.

Any water intrusion in the rear wall will accentuate the buckling. Your last line says " don't see any leaks or evidence of past leaks anywhere inside or out except on the back wall?" So you do have a water leak?