From Wikipedia
http://en.wikipedia.org/wiki/Candle#Fuel_and_c andle_holders
A candle typically produces about 13 lumens of visible light and 40 watts of heat, although this can vary depending primarily on the characteristics of the candle wick. For comparison, note that a 40 watt incandescent light bulb produces approximately 500 lumens for the same amount of power. The modern SI unit of luminous intensity, the candela, was based on an older unit called the candlepower, which represented the luminous intensity emitted by a candle made to particular specifications (a "standard candle"). The modern unit is defined in a more precise and repeatable way, but was chosen such that a candle's luminous intensity is still about one candela.
You could probably make this work more efficiently by using a radiating device such as the one suggested above. You should also bear in mind the fire risk aspect involving candles as well as the risk posed by the hot wax. Candles also release smoke and after a few years the inside of your camper will become coated with the smoke residue.