I was in the same boat and installed one of these, no power is required and they work great
http://www.amazon.com/Camco-57331-Olympian-Wave-3-Catalytic/dp/B000BUV1RK
then later I also purchased a larger Cat 6 because my Class B is not so well insulated. That would depend on how well insulated your camper is. At that time of year I would go with the cat 6 wave heater you can always turn it down if its too warm
I also installed a solar panel on my roof and that's the best thing I have done for my camper...not tied to any campgrounds anymore.