My Ole Toy-house had a 20 lb horizontal tank (looked like a regular BBQ tank mounted sideways). We carried a 20 lb BBQ tank and when stopping for more than a day or so, would disconnect the horizontal and hook up the BBQ tank (Its easier to get the BBQ tank refilled than the horizontal tank)
Anyway, we would store it under the bench seat. just make sure its completely off when storing and also have a propane detector/alarm.
2001 Coachmen Mirada (Ford F53 6.8L V10) - Toad 2001 Civic
It won't do MACH 2, but I can get a sandwich and take a pee.