Harold,
I took a brief look at the Cheap Heat system and agree with you - it's could be a good addition to an RV that already has a well-installed ducted propane furnace system.
Space electric heaters do not distribute heat throughout the RV anywhere near as well as a normal ducted furnace system does. Why not use the propane furnace's duct system and it's fan - but run it electrically when you can off hookups instead off propane. That makes good sense to me. Our propane furnace's ducts keep the fresh water system piping warm in behind the cabinets and structure voids ... and in extreme cold this protection can be priceless. Space heaters cannot do this well ... especially with respect to interior hidden voids where merely opening cabinet doors won't get warm air back into them.
It also adds very effective backup to an important RV system - it's main furnace. In the unlikely case of a propane system failure or fuel run-out if ever caught out in cold weather when drycamping, you can just fire up a generator to keep a ducted heating system operational with hardly a break in your warmth comfort level or interior piping freeze protection.