Many hot water heaters have "by-pass" valves for winterizing. In by-pass mode, cold water by-passes the water heater and goes straight to the faucets. This allows the hot water tank to be drained for the winter and saves on the cost of the pink anti-freeze that's pumped through the water lines to keep them from freezing and cracking over the winter. It makes it a lot easier to flush out the system in the spring to purge the pink stuff before you begin using it too.
Check to make sure your water heater isn't by-passed.
Many hot water heaters have both an electric heater element and of course the propane heater that comes with all of them. The two different heater have separate switches and can both be used at the same time for a quicker warm up.
Sorry I don't have anything specific for your RV though.