This may or may not apply to your Atwood furnace, but there are a couple models that had the circuit board mounted horizontally, with one edge pushing against the inside of the furnace door/cover. My furnace door leaked along the top and water ran down the inside and onto the circuit board. That caused my blower to turn on continuously, even with the thermostat off. This happened on a cross-country trip, and pulling the fuse would shut things down, but since it was the SAME fuse as the refrigerator, that quit also. I ended up drying the board and placing it in a zip-lock bag before sliding it back in place. I also put some painter tape along the top of the door panel to keep the water out until I could upgrade the seal. Ultimately, Atwood replaced the furnace because of an unrelated issue, and the replacement had the board relocated, and included an updated door/cover. Also, it is easy to get water into the heat exchanger via the exhaust pipe when the units are mounted in a horizontal position. If you look into the exhaust you MAY see it leads in a downward direction into the heat chamber. The factory says any moisture will burn away when the furnace runs. I say it will sit in there all summer and cause rust. Time will tell. Most of these units are pretty nicely built and work great, but with all the various mounting possibilities by the RV mfgrs, anything can happen.
2009 GMC Sierra 1500HD 5.3 Bells and Whistles
2015 Dutchmen Kodiak 263RLSL