When we use (need) a space heater, we simply plug it into an outlet...in the kitchen area where we have a 20 AMP GFI. Never a problem. On the very rare occasion where the temp can get down to F20 or even below, we use both the propane and the space heater....once, at 14 degrees, open the bottom kitchen cabinets and aim the space heater there. Hopefully, keeps the pipes from freezing.
Want to "save" money by not buying propane? Not good. If no shore power, make sure your batteries are good, they should power the propane heater all nite. Have a generator? Start it up and you can run both the space and propane heater.