More info on your camper will help, but no, i do not believe the electric side of your water heater would be automatic. If you leave it on all the time, and drain it (either through its drain or by running out of water) you will burn the element up. There may be a small switch under the outside cover to turn it off.
The tank heater switch is most likely to turn on the pad heaters on your black, grey, and fresh water tanks to help prevent freezing in cold weather.
Btw, welcome To the forum !
Joel and Teresa
2016 Sabre 34TBOK
2006 GMC 3500 CC LB DRW 4X4