The way to do this is:
1. run a line from the hot water feed at the faucet to the cold water intake on the hot water heater.
2. put a one way flapper valve in this return line so the open side feeds the cold water inlet connection.
How it works: Hot water goes to the faucet and sits there. As it cools it sinks thru the flapper valve an to the cold water feed line of the hot water heater. The flapper prevents cold water from going up to the hot water faucet. It works very well in a home situation by convection cooling but not sure how it would work in an RV.
