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 ...
My guess is that someone working on the trailer has left some butts in it, in some place that is not obvious. Take it apart with a fine-tooth comb... under the bed, under the dinette seats/furniture, every drawer, cabinet, the space around the water heater, the wardrobe, medicine cabinet, anywhere else they might have been into.
And if you can't find it, take it back to the shop.