02/propane alarm keeps going off

I also have a Safe T Alert combo unit. Over the last 14 months or so that I've owned this MH, the propane alarm has gone off 4 or 5 times. My issue is linked to the water heater operation. The only times the alarm has sounded, have been when the water heater is on, or has been recently shut off. All connections have been checked and seem to be fine.It is believed that the fumes from the water heater, under the right conditions, are rising and entering the MH through the over the range exhaust vent, which is directly above the water heater. The outside vent cover is not a solid flap which can be closed, but rather a fabric flap. Since this idea of the cause of the alarm sounding, I have used the water heater 3 or 4 times, with the exhaust fan running, and the alarm has not sounded. Hopefully that vent location was the reason for my alarm sounding, although it remains to be seen, since it was so infrequently that it sounded anyway.