What is the difference between the generators that are mounted underneath the bus and a portable generator? Is it possible to mount a portable generator? Other than extending the exhaust to exit properly, what else is different? I found a great deal on a propane powered generator, but it is a 'portable' unit designed to run off of a standard 20lb LP tank. I would like to be able to run it off of my existing LP fuel tank that the bus runs off of, and I don't really want to pull it out just to fire it up if possible.