i know this is a bit overkill and too heavy for solo's, but for extreme cold weather useage on an outfit, I have a 12v switched/fused socket in the chair, and connect this to an insulated ammobox, containing all the battery chargers,ipod, lighting etc for use in the tent, together with a 7AH gell cell.
Charge it when running, and hey presto, enough 12v power in the tent for the long scandanavian winter nights, cos li-ion and nicads die quickly at -20c.
The chargers/cameras/ipod/ valuables are kept safe if the weather is lousy, and boy did it rain this january!!!!
The most effective way of turning petrol into noise without the side-effect of horsepower