Cold weather travelling in Class A

We have an extra heater that runs off our engine heat in the bedroom. This is in our older HR Endeavour. Works quite well although we to have a remote senor in the wet bay and if needed fire the furnace up. So far all has worked well down to around -11C or 12 F. Much below that and we might need some extra heat in the basement. The coach itself was quite comfortable. These old gals were pretty well made. It is a 1997.