I believe the only way for the water to get in is around the rear window, around the rear fiberglas cap where it joins to the roof, past the ladder mounts, or past the seals for the storage compartments. I mean if they are all sealed correctly you should have no leaks. I agree that you should check for any leak spot in those areas, primarily where the cap joins the roof or around the ladder mounts, and try to reseal the area with the proper sealant. These areas seem most logical since your leaks come down the wall. The rear window is also a logical area, but can probably only be visually inspected. For puddling in the rear storage compartment on the passenger side of the RV, check your water pump. I found the screws that attach the water pump to the electric motor loosened after a few years. I tightened them all again, just slightly, and the puddling stopped.