Since you are gutting the interior and starting over, I agree with the other comments that mold inside the walls and rotten structural wood will be your primary focus. Do as previously suggested. The signs to watch for are interior water stains (especially in the front over-head cab) and the smell of mold. Stand on the floor around plumbing fixtures and bounce yourself a little to see if the floor is soft. Replacing or repairing a rotten floor will be difficult. If your rehab includes removing the interior wall board, that would be a good thing so you can kill any mold, replace rotten studs and ceiling rafters, update the wiring, and insulate better. Nobody will insulate as good as you. I personally would insulate using 1" foam board. Cut to a compression fit and touch-up voids with spray foam. That will yield best insulation results.
