No doubt heat pumps are much more energy efficient in mild (cool) temperatures, but cost efficiency to RV owner can vary significantly.
If at campgrounds where electricity is included, then running a simpler electric heater or multiple small units is no more expensive. And if running generator solely to power the heat pump, then using propane is probably cheaper, and likely safer at night.
Full timers who pay for their own electricity, or those connecting at home to keep unit warm, may benefit the most from heat pumps. I would not use one enough to make it worth the cost or added complexity.