i placed 100 watt severe duty light bulbs in all the basement compartments, guarded by wire cages. the bulbs are commonly used in garage extension lights.
i have a tankless water heater, and place a bulb in there also. anywhere there would be a danger of freezing.i used a total of six bulbs
ive been in below freezing weather in montana in january, and didnt freeze up.
there is no way to really stay warm in a motorhome in montana during winter. you survive, thats all. electric blankets are a real life saver.