I do not recommend burning propane INSIDE a closed vehicle. many have done so, many have forgotten to wake up come morning.
now opening a window may get you enough O2 to survive but this runs up the heating bill.. Better to use a proper VENTED Rv type furnace, it runs off your big bottles and will last several nights on 25 pounds.. Takes up no floor space, No tip over danger. and provided the heat exchanger is in good condition no CO danger either.. Have a good CO detector in case the heat exchanger gets religion. (Becomes holey)