External Heating Method?

So, due to me possibly leaving my tank for an extended period of time (1 week max), I wish to limit the possible risks to the tank.



I currently have no heater, due to my canopy keeping the tank warm, but winter is coming and I need to prepare.





Is there any way, perhaps already done, that I can heat the tank from the outside. Perhaps some sort of heat pad/tape, placed on the back glass?