Dometic thermostat and control box

BFL13 thank you, that does seem to more closely match what's going on. The furnace does flame on, and burn for a few minutes, sending hot air into the "house" and hot exhaust out the exhaust port. I just checked and the heat at the exhaust does slowly fade as it runs until it shuts down.

I will check the propane pressure and gas valve.

Thanks again.