I know you are trying to sort out why the heating elements in your AC do not work but we found out in a previous camper a portable electric heater is capable of putting out the same amount of heat as the AC heating coils. The small portable heaters are typically much quieter and allow you to move the heat to where you need it most. These are relatively cheap and available from many sources including Walmart.
I totally agree. Heat from below, placed in front of where the cold comes in from worst which is the cab area, does a much better job and so quietly too.
Still, it would be nice to have the roof heater working, assuming you have one. If you don't have one, I don't think you are missing much at all. As I recall, our heat strip was optional. Back in 2007, I think we paid extra for it, but it might have been part of the "Premium Convenience Package" back then.