Heat will go out after hours of use

We have never stayed in temps as cold as you are in, but from reading on these forums, it is known that the absorption refrigerators do not operate properly in cold temps. Many hook up a light bulb in the exterior access to help keep it warm enough to work. If the flame goes out, the gas probably shuts off as a safety feature. On the furnace - guessing that maybe after running for so long it overheats, and also a safety feature that it shuts down for awhile to cool off. I do know that our Atwood also has a 1 hr time period if gas valve shuts off because of no propane. Is the pressure regulator maybe going out and when pressure is low, gas valve shuts for the 1 hr lockout. Just guessing at a possible cause based on things ours has done Many problems we have had with any of the gas/electric appliances has been corrected by checking and clean electrical connections make sure everything is tight and cleaning burners, etc. We also had a problem one time when there was a crispy fried mouse near/on the burner area. Remove the mouse and furnace than ran like it should. Have you looked online for a manual and troubleshooting for your particular brand/model furnace. They are very helpful with diagnosis sometimes.