On board furnace runs on propane but often has a circuit board and 2 fans. One fan to blow the exhaust out and another to circulate the hot air inside the rig. They often draw about 5 or 6 amps.
120 volt electric space heaters can be bought for $20.00 or so but you have to be plugged in or running a generator. Many electric space heaters use about 1200 watts or so. 1200 watts divided by 120 volts = 10 amps. A Honda 2000 will carry about 15 amps max.
It can be run on solar but it's not practical as you run out of room for batteries and panels. I dont know the figures right off but running a generator is probably about 10 or 15 times as expensive as plugging into the grid. Just a guesstimate from what people have posted.
To me, rv equals moderate climate and moving with the seasons.