To MPM:
Can you post a photo of the exact spot where you sealed up
To WHEELPDLR:
I went from the bottom, but I did not have to cut anything except the thin plastic layer and polystyrene. I cut the plastic in such a way that I could fold it back after, and have another layer of thin plastic seal it up again. Then I pulled of the soggy fake wood, cut with a hand held blade through the polystyrene, pulled of the next fake wood layer just beneath the linoleum flooring.
The wood supports could basically lie down on top of the camper support beam on one side, between the aluminium square tubing that makes up the floor, since I removed the polystyrene in those locations.
This is now the strongest spot in the camper.
It was not hard, but it depends on the area you have to fix. If it was at a different location, I may have had to go through the top.
But yes, do not just cut with a saws all.
And yes, even after several rains now, the camper stays dry
