This answer to how much heat (in BTU's) does a candle produce seems pretty accurate, as does the admonishment of the firefighter that posted not to be an idiot and have lit candles while you are sleeping.
Woodalls Open Roads Forum: Looking for ACTUAL MEASUREMENT ( no guesses...) What's the BTU output of a candle?
I would say a decent candle lantern, one with a chimney such as an old kerosene lamp would have, burning a good sized candle might (if your lucky) produce the heat and light
of a 60 watt light
bulb. Bees wax candles don't produce much soot. A tea candle would be more like a 20 or 40 watt light
I do know that the large candle burning in a coffee can will raise the temp inside a car by a decent amount from using the one in my snow emergency kit from the trunk. Difference of about 10 degrees above outside temp. But that is a small space and a big candle.
I guess if you were up doing whatever in your camper candle lantern would make a cozy light and maybe keep your heater from running as often or take the chill off a cool summer night. But only while your awake! And not near curtains.
For sleeping I go with letting the dog or the wife under the covers, whichever seems most inclined to cuddle with me at the time.