I bought a 1992 Buick Skylark about a week ago. It had mold all over the interior and water on the driver side floorboards front and back. I had it cleaned and fogged. The water on the floorboards was gone but remained damp. the next day the water was starting to get worse. I haven't run the a/c at all and it has not rained in a few days.
Water on 1992 Buick Skylark
Had the same issue with a 1993. Remove Wiper arms, cowl and look inside, you'll will probably see body sealant moved away from a seam, seal them up with some kind of sealant, silicone etc and make sure drain holes are not clogged. This should resolve that issue.
cheak your window seals.
It can take a long time to totally fry out the interior of the vehicle, and you also need to make sure there no water still leaking into the interior. If you have a plugged drain in a door, or a sunroof, water can continue to seep into the interior. It's best to take out all the wet carpeting, seats and interior panels and let the car dry for as long as it take.