Hi,
I've had to resize each photo here. I hope you gearheads are worth it...
Someone must have spilled gas in the box of this thing or used some kind of chem to try and kill the carpenter ants. The box is a fiberglass, wood, foam, and plywood sandwich with a layer of aluminum sheet on the steel frames rails in the floor assembly. The foam has melted in a bunch of spots in the rear floor and walls around the doors. Nowhere near the exhaust.
I cut straight edges into the plywood with and oscillating saw to get at the melted foam and cut out the rotten wood.
I had a local tin basher bend up some heavy gauge galvanized sheet steel to replace the paper thin aluminum in the areas I worked on. Lots of caulking in the corners and on top of the frame rails. Three pieces to make the installation easy.