I'm not familiar with your particular trailer but my hot water heater has an electric switch (rocker panel switch) behind the external access door to the hot water heater. It is a black switch located on the back wall of the heater compartment near the bottom left. I start off with propane, turn on the electric and then turn off the propane after about 20 minutes. My hot water heater has a propane switch inside along with all the other light switches, awning, slide controls.
Randy and Patty
2015 Sabre 33 CKTS-6 Platinum Edition
Reese 16K Slider hitch
2014 Ram 2500HD Crew Cab 6.7 Cummins Diesel