Hi Rusty,
I filled the 60 pound propane tank twice in 2014. I do space heating, water heating, and cook 100% electrically. If you can get a cheap heat that comes "for free" by all means use it. As I have a 30 amp service on my RV the cheap heat is not be able to provide all the heating needed. It is unable to be used as supplemental heat to the propane furnace. At -37 C I need 6000 watts of electric heat to keep warm. The other big issue for me personally is lack of fail over to the propane furnace. Everyone's situation is different and I'm glad the cheap heat works for you.
I do have a way to keep the basement warm which only uses 23 watts of power.
I boondock for months at a time, so my major propane use is for the fridge.
It would require filling the propane tank about every three days at -37 C to keep the RV warm. Gotta love any form of electric heat--but I do need about 45 amps to do so. I love the fireplace idea and wish I could find space for one.