Back in the 80s a buddy of mine had a van that ran on propane. It ran fine and had decent power.. and was cheap. I didn't like the fact that he had taken out the seats for space and i had to sit on the tank which was mounted to the floor. I think he had it mounted inside because it was pretty big... I'm guess maybe 100 gallons. Probably so he could go long distances with propane stations being so infrequent.
Yeah.. I'm looking at my 90 gallon fish tank and that looks to be about the same size as the tank in his van.
Back to the power issue... he lived on top of a 1 mile high mountain and it got up there every day with no issues.