[JRTJH]

The rear wall is a "free hanging FILON sheet. It is held in place around the edges, the tail lights, license plate light/bracket and any vents/windows that might be on the rear wall. Otherwise, it's "free floating" and will "oil can" (buckle/bulge) when exposed to hot sunshine.

Here's the only photos I have handy of the way Keystone builds the rear wall. The aluminum framework is secured to the sidewalls/floor, then the interior wall is installed, insulation/wiring is installed and finally the rear FILON is attached and the molding is applied to the edges all the way around the rear structure.