Just as a follow-up, and in case anyone else is having a similar problem, I was successful in getting the electrical side of my WH back in operation. When I removed the access cover on the inside face of the heater (--- the box/cover with the toggle switch on it) I was surprised to find that the entire electrical heating element apparatus, including the ECO, the thermostat, and the element itself, was located under this cover. Apparently the 120 volt electrical side of the heater has no relationship whatsoever to the propane side. With both switches on (---the wall switch as well as the toggle switch on the box) there was no power at the heating element connections - although I had power up to the box from the wall switch. The ECO is a tiny unit with the "reset" button located between the spade connectors (---that wasn't obvious looking through the "pencil hole" provided in the cover.) I turned off both switches and, after depressing the ECO "reset" button several times - with no "audible" response - I ran a continuity check across the spade terminals and got positive results. I then ran the same continuity check on the thermostat (---which looks just like the ECO) and the heating element itself - and I got positive results on both of those units. From there I ran a complete continuity check on the wiring harness, up to the toggle switch on the box, and that too gave a positive result. At that point I turned both of the switches back on and checked the terminals of the element. Hooray - I got a good 120 volt reading! Now I'm not sure if I had a corrosion problem - or if the ECO reset switch was not re-engaged. For the record, I had completely removed the ECO switch from the mounting plate when I was checking the reset button. Surprisingly, when I depressed the button against an apparent spring resistance I lost continuity, but, when I released it, continuity was restored. That seems sort of backward to me but regardless, when I checked this morning I had plenty of hot water!
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074