Hi suncamper,
We didn't hear from you in so long I thought you must have resolved the problem. I'm not too familiar with Atwood water heaters; perhaps they don't have the rocker switch that's found on Suburbans.
If you've got a Voltmeter and are comfortable working with 110V wiring, you can probably do some diagnosis yourself. If you test voltage at the heating element terminals (probably underneath a cover), you ought to have 110V when the inside switch is turned on.
If you have voltage there, you may have a burned out heating element, which can be caused by turning the electric side on without first filling the water heater with water. For example, when you have the trailer winterized, the water heater is drained. If someone turns the electric switch on, the element will be burned up.
If you don't have 110V at the element, the ECO (electric cut off) breaker may have tripped. You can try pushing the reset button.
If you still have no voltage, you'll have to check the voltage at all points between the inside switch and the heating element. I think there may be a relay somewhere between the inside switch and the water heater circuit board, probably behind the inside switch.
Or you can take it to your dealer. It may still be in warranty. The water heater may have a multi-year warranty.