Put the burning candles under the truck.
It will create more heat.
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Buy a nice high quality goose down (not duck down) sleeping bag from Western Mountaineering or Feathered Friends. Buy once and sleep warm forever.
Candles are common as a last resort emergency warmth source for cavers.
Another option is boiling water and putting it in a nalgene. Sleep with it between you legs for added heat. (aka beaver bottle).