erip - Your signature or profile does not give us any clue as to what you are driving, but if I recall you bought an Augusta Sport model 210. That floor plan is the same as my Trail-Lite model 211 with a rear door. A leak in the rear door windows is strange. I don't even know how that door is constructed. If it is the same as the side walls, you shouldn't have too much to worry about internal rot or rust. Nevertheless, I would "bug" the dealership about getting a new door. You would not want some metal parts in the door to start rusting. The sidewalls are plastic, fiberglass, aluminum and foam insulation, but the door has the lock mechanism.