Perhaps put the chemical hand warmers under the blankets? And you can buy battery powered air too. In another thread we talked about this a little bit. One person said to buy the battery powered air that are used for live bait as they are like 10 bucks instead of the 80 dollar price for the ones they sell for pets.
Also, keep the tanks on a piece of foam, its insulative, will help both ways. Hmm. I wonder if you could use the foil-bubble-foil insulation? Perhaps have a pre-built box, lined with it, and put the tanks in the box.
It shouldnt touch the box or the tanks though, needs space to reflect all back the way it came. Could work and may be useful if the power was out for really long periods.