We looked at many used fifth wheels before purchasing the one we have. Most significant issue in the used units we checked was water damage. The damage wasn't visible but only apparent with some prodding and poking into walls and floors.
With one of the units, the dealer said a "soft spot" under dinette seat. That "spot" turned out to be from a pinpoint of a hole where the rubber roof met the back wall. Half the back wall was rotten, then the water pooled at the floor and rotted out 6' of floor on the one side. My thumb pressed through the interior back wall it was so soft. The floor damage was under cabinets and the fridge, but by pulling out the drawer under the fridge I saw the wet. And then I poked into the outside hatches and saw more water damage under this area. The dealer offered to fix it all before we bought but I wasn't interested at any price. Way too much wrong.
We had rebuilt the upper bunk of a motorhome for the inlaws when a window had a small leak over years and years. The water pooled under the bunk and then rotted the wall areas. Wood rot isn't fun to deal with, and often hard to detect until you open the wall.
