You guys are starting to worry me with all this talk of Gerry-rigging
unvented heating devices.  Now stop trying to replicate the toasty warm
comfort of your bedroom and enjoy the great outdoors for what they are from
inside a decent sleeping bag.  Eat a lot of fat, wear a watch cap, take a
whiz, change into fresh dry skivvies before you bed down and you will be
surprised how warm you will be.

If you still want the heat, why not leave the hydrocarbons outside by using
one of those miniature Honda generators and dedicate it to a resistive space
heater inside?

Rich