i met an interesting fellow last year at an alternative energy fair in northern n.y. that would solve the problem of a block heater for those with limited or no electricity. the design of the heater was basicly 1 steel pipe surrounded by another larger steel pipe. the smaller pipe served as the firebox. the larger pipe served as the watercoolant jacket that as the temperature increased it would thermosiphon back to the engine via 2 quick connect fittings spliced into the coolant lines. he also had hooked up a 12 volt pump to help the whole process along. this is the same process loggers use in the winter to get there skidders started but istead of using a wood burner they simply pull up with their truck and connect there coolant hoses to the skidders hoses with the quick connect fittings. the whole woodburner was small enough to be picked up with ease and set into the trunk if need be.