The honda has a vent cap that leaks no fumes.I always carry it just inside the door and there is never a hint of a gas smell when the vent cap is in the off position.
For a gas can,my camper does not have a basement and I can carry gas in one of the wheel wells or the outside storage compartment.I just use a gas can used for chainsaws in 1 or 2 gallon size for the generator.They are a rugged gas can even though they are a plastic of some sort.
If I had a basement TC,I would be looking for a ladder rack of some sort or a cheap hitch haul like what is used on ATV's that are smaller and go upward from the hitch.