Hi,
Do not forget to protect your fridge if the temperature will be below -4 c (20 f).
I use:
electric heated carpets
1/2 size oil filled heaters tucked away in otherwise unused space
600 watt fan based heater for the waste tanks on a mechanical thermostat
60 watt bulb in the exterior fridge vent controlled by a thermocube. I do restrict the air flow by taping off two of the three vents.
I replaced the cold air return for the furnace with dual window fans. They are controlled by a mechanical thermostat and happily for me, do flow some air through the furnace duct work. This prevents interior water lines from freezing. If the furnace has a duct to the basement it would keep that area from freeze up as well. My waste tanks are enclosed but someone at the factory forgot the connection to the furnace which is why I have the 600 watt heater.
I use an electric mattress pad for comfort reasons.
I've used this configuration at -37 c (-34 f).
At those temperatures the peak demand was 7000 watts, so a 50 amp service is needed. I have added 2 auxiliary shore power cords, and use a break out box on the 50 amp pedestal.
I leave the propane furnace on as a back up should the power fail.
