The electrical unit switch which is located in the lower left hand corner of the water heater and is accessible from the outside of the trailer is notorious for failing or being difficult to operate . The switch on our Casita failed and needed to be replaced. The switch on our Escape was sticking , so I cleaned and lubricated it and after exercising the switch ,it finally loosened up
The switch is not designed to connect or disconnect the water heater under load , it is a work / safety switch
I added a single pole 20 amp switch with pilot light in the interior of our trailer at an easily accessible location and leave the unit switch in the on position