Run some searches for body drains or water leaks. Water must follow drain channels through the body and exit out the drains in the bottom of the body. The drains look like rubber nipples if you look under the sides of the car. Check the manual at skinnerbox. I bet this is also mentioned in the FAQ sticky threads in this forum. If your body is already rusted out this may not help you.

http://www.peachparts.com/shopforum/search.php