A house water heater is in only equivalent to a RV water heater in that they both heat water. That's where the similarity ends.
You only have 6-10 gallons of water in your RV heater, and a gas burner that uses huge amounts of propane to get that water up to temp quickly. BUT, it only takes a few minutes to do so. Between 5 and 15 minutes. That water loses heat quickly too as the tank is small and somewhat exposed to ambient temps near the skin of the RV. And when that happens, the propane burner pops on and brings it back to temp whether you're using water or not. This is especially noticeable during cold weather.
It is basically a waste of propane to leave it on all the time. Just flip on the switch 5-15 minutes before you need hot water, and flip if off after.
Many owners have wired in an after market electric heater that goes into the drain hole for the tank in order to
save on propane. Very handy, and gives you hot water whenever you need it when parked and plugged in. Hott Rod is one of those.
