I found an easy solution, at least for me, to turning on the water heater on electric without going outside or flipping the breaker on/off.
There is a remote control adapter normally sold to control outdoor Christmas lights that works like a charm. The specs for the adapter: 3-wire, 120 volts, 15 amps, 1875 watts. The specs for the water heater are 3-wire, 120 volts, 12 amps, 1440 watts. It's a match made in heaven. Just unplug the WH, plug in the adapter and then the WH to the adapter. Easy as pie.
In my TT the water heater electric plug is easily accessible under the sink cabinet. In some rigs it will be more difficult to access.
Now I can turn my water heater electric element on/off with a push of a button!
The adapter is the Stanley model 31171 (less than $20).