since you don't list the year or model of popup, nor the make and model of the furnace, posting pics of what you're talking about would be very helpful.
that said, your furnace is heated with propane and has no electric heat. you haven't mentioned if you have the tanks full of propane.
the furnace fan is run by 12v power, which can come from the battery or from the converter.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC