If you suspect the water is coming up through the belly pan you should fix those leaks right away as you have insulation between the belly pan and your sub-floor and the insulation will hold water for quite sometime.
I am in the process of repairing an AS I just purchased (1985 Sovereign
25'). The belly pans in the rear, same place the rotted out floor was, were full of holes and about to fall off. I bought some 2"W x 1/8"T aluminum from Lowes and cut it into 2" and 1" squares. Proceeded to carry those pieces under the rear of the camper and stitched the entire belly pan from the rear axle to the bumper. I used a big button rivet and utilized the factory hole by drilling out the old rivet. Each rivet hole was slathered with Vulcum before the rivet was popped. After the refabing the belly pan I applied panel sealant I purchased from the local auto store to help seal the seams. As an added benefit, when I replaced the sud-floor I attached Protex insulation to the plywood. I figure this will benefit me in 2 ways, 1) obviously the insulation factor and 2) giving the undersurface of the plywood more protection from the elements without holding water that may get in there. If you like I can send you pics of my repair. Just send me a PM.
Working on the belly pan is not fun at all. You will be sore and extremely dirty as everything nasty that is in or outside your trailer will accumulate there. It took me approx. 8 hours to complete the job myself. However this is the first day in the last three that I havent felt pain from doing it.