Not sure what the above posts are referring to but factory camper furnace/heaters are exhausted to the outside as evidenced by the vents that get hot outside.
We use an electric heater (when we have hookups, obviously ) that has a thermostat .
We set the 1500 watt electric heater thermo on 65 degrees and the factory camper heater on 60.
When pretty cold outside the electric cant keep up and the temp drops to 60 and the furnace comes on .
Both running together at 59 degrees they are quick to raise the temps and the furnace shuts off.
This has worked in our hybrid with tent ends open in mid 20 degree temps
Good Luck, Mike