Our previous motorhome had the duel electric element Aqua-Hot system. Worked perfectly. I used to have it serviced yearly until I saw the nozzle that was taken out, it looked brand spanking new! So, I went to a two year service interval and probably could have gone longer like Ivylog.
The new motorhome has the Webasto heating unit that is very similar to Aqua-Hot as it circulates antifreeze through the engine, etc. We also have a 20 gallon water heater and a tankless hot water heater for the shower.
I have not used the roof heat pumps yet. We have electric toe-kick heaters (2) and heated floors. That seems to work fine so far.
MM.