We had a mushy floor in our PUP, near the back wall. The floor turned out to be rotted from having gotten soggy. We never found where the water came from, but since the camper was used and not under warranty, we cut out the bad place and inserted new flooring. Then used waterproffing on the underside, and filled all cracks with waterproof foam insulation. So far, we seem to have solved the problem--no more mush and no sign of a leak. I think the floor was originally cut a bit short and water from the road splashed up inside the trailer inside a seat-storage area and couldn't dry out--hence the rot.