Sterno is methyl alcohol with gelling agents put into it. Its the pink stuff you see under chaffing dishes and the like. I'm not sure it's warm enough to do much as far as heating goes, and if it spills (the part that is burning is liquefied) in a vehicle interior, your best bet is to bail out and grab the extinguisher as you go.

There is another thread around here somewhere about 12V appliances, including heaters, although I do like the idea of using a catalytic heater as it won't draw down your battery but you do need to be worried about ventilation.

Speaking of insulation, how much is under the dog crates? More of that, even if it is two inches of closed cell foam (used for upholstry work, even salvaged couch cushions will work), will keep them warmer. And if they aren't claustrophobic, a BIG blanket or two that can go over you and the crates will keep all of you a little more toasty.