Hot bikes do smell and I think there is a little gas venting going on there. Typically I don't put a hot bike in the Toy Hauler but even just driving it in and shutting it off you will get some exhaust smell.
Personally I prefer a separate garage, kinda like a man cave... You can actually go as low as 25' Toy Hauler with a separate garage. Where they start getting longer is if you want a front walk around bed and a separate garage then your probably looking at 30'+.
If I was searching I would first pick a price.
Decide on Bumper Pull TT or Fifth Wheel. The size of your truck will come into play here. Then include separate garage in your search.