Our last camper was bought used from someone who used it very little. He had documented annual roof treatments from the dealer. It was well taken care of. I looked it over VERY carefully before buying.
Fast forward one year, I was fixing some (self induced) damage and discovered the entire back wall was rotted. No signs of any repair or cover up attempts. I firmly believe the PO didn't know about it nor did I for the first year I had it. I might would have sold it not knowing myself if I hadn't had to dig into it.
I've also bought new and had leaks from day one!
Two types of campers out there:
One's that have leaked.
One's that are going to leak.