Sounds like one I had several years ago. Mine had a switch for the electric both inside the trailer and one on the back of the heater I didn't know was there. We also smelled a burning smell and traced it to the heater. When we returned home I removed the water heater to find the switch mounted on the back of the heater had melted and had burnt the insulation partly off the wires going to it. The insulation in back of the heater had like black soot on it. It might have came real close to causing a fire. In my case there was no way to see behind the heater without removing it.