After a lot of research, I installed a heat strip in my A/C unit.  It gives me additional free heat at the campsite, better circulation, and hides the exterior noise when the kids are sleeping.  It does not replace the furnace or other heating source but provides 5600 BTU, usually a separate circuit so eliminates breakers tripping.

The coleman/RVP air conditioning units have new knobs with the unit and thermostat control.  The DuoTherm/Dometic units do not have thermostat control and is not recommended to be run for more than 4 hours at a time.

FYI - it costs about $45 and can be installed is 2 screws and one plug.

http://www.adventurerv.net/col.....p-708.html

Worth the money