I recently endured a 10 day power outage following hurricane sandy. The outage resulted in heat dropping the temps in my house to 42 degrees. But I did have hot water!
I moved both fish tanks to the basement which was about 10 degrees warmer than the rest of the house. I placed 2 layers of towels under the tanks and then wrapped each tank with 2 large towels and 2 fleeces each. Inside the tanks I used 2 poland spring bottles with gravel and hot water to keep things heated. I did 2 25-30% water changes daily (morning & evening) with hot water conditioned with Stress Coat.
This all managed to keep the tanks between 74-78 degrees. I realize the fluctuation was larger than the fish are used to but they both survived and are doing really well now.
I thought I would share my experience in the event others face a similar emergency situation. In my case I was unable to relocate as even local hotels were without power.