Back in the 70s gas crunch, I converted my pickup to run on propane (or gas). I had an 80 gallon tank crossways in the bed. It took up a lot of room, but with the propane and gas together I was able to get to the Lake Tahoe ski areas and back from San Jose. For a motorhome you would need a much larger tank, and even the 80 gallon unit I had would be hard to locate in a motorhome.