I wonder if it is just coincidence, but we have the exact same camper (212 QBW) we picked up in November. We had our first outing this last weekend, and also are having a hot water heater issue. Ours worked the first time, like yours, but did not come back on again. I did some trouble shooting at home last night, and discovered the gas valve turns on, but the igniter will not fire. I know there is gas, because I can light it with a match when it tries to turn on, but the valve will still close. The igniter doubles as a flame sensor, which appears is not working either. I spoke to the dealer this morning, and indeed they are backed up to the end of May. I am going to do some more troubleshooting on my own. Right now I'm thinking it is the control board.
If you also run into an issue with the A/C not cooling properly, I know how to fix that one.