I'd be willing to bet there's a small, undiscovered leak somewhere that has gotten the carpet or curtains wet. We kept noticing the "smell" year before last and finally found a couple of potentially bad leaks that had soaked the carpet under the bed, in the back closet and in the passenger side floorboard. We fixed the leaks, pulled all the carpet/padding out and replaced it with FLOR brand carpet squares, got rid of the old jack-knife sofa and the padded dinnette set. Replaced the sofa with a futon and put it where the dinette set was, and built shelving where the old sofa was. No more smells and a happily renovated motorhome!