Hi Jerry,
I just wanted to add that your spare parts advice is dead on.
Through the volt meter and domestic/Atwood troubleshooting guide, I was convinced my DSI light and lack of gas heat was the circuit board. Replaced it with a dinosaur board (btw, much better card- lights quicker, stronger spark, better construction A+), only to have it occasionally not light. Traced the intermittent problem to both cheapo thermostats. A little wiggle of the wires and boom, everything lights off great.

Circuit board, igniter, thermocoupler, or thermostats. 99% of your gas water heater problems are going to be in these components.

Very much appreciate the thread advice.