BillyBob Jim wrote:
It would be next to impossible for CO to find its way inside the rig from the water heater. You would need to have a huge hole somewhere in the sidewall, a large gap around the water heater mounting flange itself, or some off the wall condition where its coming in through a window or vent. I would guess a defective alarm as the ones used by the OEMS are the cheapest obtainable.
You don't have a farting dog in the rig do you?
co2 is coming in thru some opening when I light the heater. 
Tested it several times. I know it’s the heater