We have people proposing use of gaseous fuels inside or venting to the cabin again...
Bad Bad Bad Bad!!!! People die from this every year due to CO poisoning.
(end of 2nd paragraph)
http://www.utahcountyonline.org/Dept...Supplement.pdf
Charles E. Kanter, AMS
If your going to use gaseous fuel for heating do it through a heat exchanger of some sort.
Your better off using electric power. If you want efficient electric heating use some thermoelectric chillers to pump heat in from outside the vehicle to the inside of it. You'll get every watt you expend plus any heat they manage to pump.