As for keeping the tank warm, do you have a fireplace to keep the tanks by? Im also pretty sure battery powered space heaters exist. Also, depending on how long power would be out for, you could try purchasing a whole bunch of those chemical heat packs. Secure them to the side of the tank and wrap the tank with those thermal safety space blankets that you would keep in the back of your car if you were taking a trip out in the boonies of alaska. That might work if you replace the packs as they cool. I think they can last close to 20 hours.