I use a candle lantern to increase van temperature 10 degrees and almost eliminate interior condensation. I also have a Buddy propane heater but I only turn it on about 10 minutes before I get out of bed. However a word of caution!! While the candle is enclosed in an all metal candle lantern, it is still an open flame; additionally, I place the lantern in a tin foil pan I got at the dollar store in case the liquid wax over flows the base of the lantern. A source of ventilation must be used, I open the roof vent. Also careful investigation must be done in selecting the candle type. I only use candles with no scents or chemical additives. Please ignore the fact that I'm wearing two different types of socks.