I have found that simply turning on the gas stove top does pretty good for heating the camper up. I do this when traveling, and the camper is cold. It warms up the camper much faster than the furnace. Well... now that I've figured out how much heat loss I'm getting under the floor, I sure understand why now.
There are those who frown on using the stove top to warm up the camper, arguing the fumes and monoxide potential. But, don't we all use our propane stoves inside the camper to cook with too? What's the difference then?
Apart from having an open flame, this is another potential for a heating source, in a pinch or if you need a fast warm up.