Not all leaks will leave stains, either. Our first TT was a 2003 Coachmen. Within 3 years, it had 4 large rotten spots in the floor with no indications at all on the walls or ceiling. I knew about one the year before because of a soft spot by the door. I found the others after pulling up the carpet from the bedroom area. I was not a happy camper. I may try to to some kind of pressure test on our new Grey Wolf this summer using a shop vac or other pressure source. I saw somewhere on here where a guy did that and built his own pressure gauge using clear tubing and water (I forget what this was called).