I might disagree with some. I bought a used Jeep that had been smoked in. Dealer promised (in writing) to negate the smell. Now a Jeep is obviously smaller then a TT, and in a TT with the mattress and carpet you might have issues.
But what they used was
Room Shockerâ„¢ ClO2 Odor Eliminator Quick Release Vapor I honestly wasn't sure it would work. But I ran the gizmo as per the instructions and I'll be damned you can not smell even the faintest smell now, even on a 110 degree day when it's closed up.
Now would I buy a TT that was smoked in? I'm not sure, but if they desmoke it first before it's too cool outside I might consider it. Otherwise I'd say walk away.