Can't give you any advise on the under bed area but I had a 1998 Palomino up to last summer. I like the camper and was almost ready to buy another one when I fell into a very clean Shadow Cruiser. Check the front edge of the roof and the front edge of the bed. I replaced the top front board twice. The first time with a strip of marine plywood, no one told me MP wasn't waterproof. Next time I ran pressure treated through planner to get the right thickness, much better. The reason I started looking for a replacement was the lower edge was going and I didn't feel like getting into it. Also check the bottom part of the door, mine was completely rotted out, I cleaned it out and put pressure treated insert in there to. I have been told that until they changed the way the roof came down over the door in the early 2000s that most have the door problem because of the way the water sheds down the back.
I got a spray mildew killer that I think is mostly clorax that worked like magic taking mildew off, don't remember the brand. Just sprayed it on let it sit for awhile wipe it off and it was mostly gone, just had to redo a couple of spots that I didn't get enough on the first time.
