our class c we can run the furnace for a day off battery, and run the gen for about an hour a few times a day, the furnace is most likely self lighting , so just turning the propane on, full, maybe light one of the burners on the stove helps purge any air in the lines i, once it burns steady turn it off, then try turning the thermostat up and see if the furnace starts, i find some times if it does not the first time turn it off ( coldest setting) wait 30sec or so and turn it back on , could take a few tries to light,,
