I went to find a link on the space blakets and found this:
Pretty sweet idea!! I may try that if I can find some at the $1 store. My local dollar does carry space blankets.
I have a few now for emergency. Last winter the heater went out, no heat for two days. I used a spas blanket over there tank to help the tank heater. Worked great, the house got down to 50degrees at night but, the tank water stayed @ 72.