There are all kind of simple ways to remind yourself of the electric heating element being on if you don't use a checklist when making/breaking camp.
One way is to just use a clothespin and write 'water heater' on it. You can attach the clothes pin to your RV's hitch coupler (if trailer so you cannot hook to TV without seeing it) or somewhere obvious on a motorhome....that reminds you turn it off. You can do the same for steps, antenna, etc.
Suburban's electric switch and much more
You can also put these below on your Christmas list if you like:
RVminders: Safety warning system for RVs