We have the strangest odor in our TT...it smells like an ash tray! (That's my best description.) We bought our TT in March, obviously used from CampingWorld and we were able to go into it and look ...
I am an x-smoker. There is a few smells that I now relate to an ashtray. One is cat spray/urine. Is it possible a cat got in and sprayed or maybe sprayed at/near the door?
Another would be slight mold/wetness.
Obviously you want to find the source, not cover it up. If you can not find it, a thorough wipe down of walls, cabinets, floors, etc.. with OdoBan (home depot) may get what your not seeing. I spray this on my dog kennel, let it soak in my black/grey tank, and it is good stuff!