I'll second what Jatrax said re. heat pumps, from what I recall from the '70's, when they were new for RVs and we had one on one of the travel trailers. One could sort of think of them as an air conditioner that can run in reverse, though to design something to do so is rather complicated and expensive. As I recall, when they were operated to heat the rv, power consumption was about the same as when set for cooling, during chilly but not cold evenings (not sure of exact cutoff, but below 40 it really wouldn't work). However, more heat could be produced than with the same power to a heat strip, so it'd cycle on less frequently. As for cost-effectiveness, they might be worth it if one frequently needed electric heat in their sweetspot of about 45+ ambient temperatures and was paying an electric bill for heating. For most RVers, not in such circumstances too long, the cheaper, simpler electric heat strip-only units or, cheaper yet, a portable electric heater, or simply the propane furnace, would be more cost-effective. I recall my father and I thought it would pencil out but actual chilly weather camping with hookups was nil, so it did not.
