Looking again at that rotted corner , That’s really AWFUL !!! I can’t imagine how water got in on the floor level , and think from all my previous experience it could only come from the roof vent ... The door had an inner dam on the floor . inner lip on the walls , drip edge over the top ...and was pretty tightly sealed . And there was only the peephole window on that side ... In the old Kustom Van days , the first place we’d look for a leak was the roof vent ...
You know the roof vent thing and moon roofs, all came from the California surfing scene.... California where it never rains ... Places that do rain, it becomes a problem .... always ... The Old Timers knew better than to cut a hole in the roof ... I think it’s done for “fashion” now .... People expect to see it because of seeing it everywhere else ... although it’s NOT the best idea ...