Leaking Ford Aerostar

I own a 1993 Ford Aeroestar extended van. Fortunately for me, I live in the Puna district of the big Island of Hawaii. Unfortunately for me, the van is now my home and it leaks (here, rain is the new snow)van leaks down the drivers rear windows, through the safety belt harness and other more mysterious places. It has all these vents and controls in back, none of which I need or use. No holes in roof. Don’t care about resale value, but how do I fix leaks, is there some central place in the vent/air systems in back that could be filled with foam? Any ideas welcome