https://www.trailmanorowners.com/for...8&postcount=34
My solution. It's a push button switch with a built-in relay so it will only switch on when 120V is available, and when you unplug the TM it automatically switches off and stays off until you push the button again. Makes it very unlikely to burn out the heating element. Ended up being a very easy install as I recall.
The switch on the outside still functions as well, but I leave it "on" all the time now -- except for winterizing.