Sounds like the same problem I had on a previous MH. I had Camping World install one of these Hott Rod Water Heater Conversion Kit - 6 Gallon - Diamond HR6 - Water Heaters - Camping World
. The installation instructions said the thermostat should be attached to the back of the tank by first cutting the insulation, then attaching the thermostat with double sided tape, then running a bead of silicone sealant around it and finally packing the insulation back on top. CW just used the double sided tape, and the thermostat fell off causing excessively hot water. It sounds like the OP has a similar after market electric heater.
Bruce Dickson 2013 Thor Challenger 37GT, 5 Star Tune, Safe-T-Plus Steering Control with Air Trim, Roadmaster front and rear Sway Bars, SuperSteer rear Track Bar, Crossfires, 2012 Honda CRV on Blue Ox Aventa LX tow bar. Full timers since Jan 2012.