I have a horse trailer, similar but different from RV. But, have been having an issue now for 2 winters with wet floor inside the door. I have been checking seals and rivet joints on the roof, looking at the door seal and underneath. Horse trailers are built different with an aluminum roof and floor, but the carpet was wet and causing other issues. Anyway, I was waxing the trailer this past week and while up on a ladder I could look over the top of the window on the door. The seal was perfect all the way around, but had decayed right over the center of the window on the top. I am certain that was the cause of my leak. I would suggest checking everything, but look closely at the seal around the window on the door or any other windows that water could run to that spot.