Are you RV'ing to save money? Do you turn off your WH in your sticks and bricks house overnight? Don't know about you, I like hot water when I turn the tap on. I like to shower WHEN I WANT to shower, I don't like to wait twenty minutes for the water to heat up. I don't like staying awake at night wondering if my water heater might freeze and cost me $$$$$$$ to fix. Honestly, If you are RV'ing to save money you should probably rethink things a little bit. The cost of heating your water 24/7 is nickles and dimes in the long run, really. YMMV
Mike