Heat pumps are not for really cold weather - as noted above, they work down to the upper 30's to 40 degrees.
Our last three RV's have had heat pumps and we used them a lot. Although some campgrounds charge extra for electric heat, most do not. Thus, one gets "free" heat using the heat pump as opposed to the propane furnaces.
On our last two RV's the heat pumps were in the basement. On our current one, the heat pumps are on the roof. I don't yet know what that will mean as far as noise level. I think I will enjoy running the front heat pump and leaving the bedroom one off, while we sleep.
Tom