Carry extra propane tank in trailer?

I’ve never needed to. Never had a problem finding a place to refill anywhere I’ve camped.

I’m not sure of any legalities, but I’d recommend not storing extra tanks in a fully enclosed space. Id your tow vehicle is a truck you could put it in the bed or convert the single tank holder on the front of your TT to a dual tank holder. But like mentioned, it’s not hard to find propane wherever you camp.

I stored an extra in our basement when we went boondocking. I doubt the basement is sealed tight enough to contain the gas if there’s a leak.