The tank would be temporarily in the garage, maybe 2 months, then into the livingroom. Regardless of how long, it does still need to be heated out there though

I can easily lash 3 sides with 1-2 inch styrofoam, same as what I'm insulating the basement foundation walls with. The bottom of the tank has plywood under the glass and inside of the trim to make the bottom flush. It sits on 1/2"-5/8" styrofoam. I will be getting glass pieces for a lid as well.
The garage is insulated and has a baseboard heater that I have on during the winter, I can turn it up. Our winters have many days below freezing but rarely that many degrees below freezing. Doubt the garage would freeze if the baseboard heater was off. It does get chilly out there so it will need more juice to heat the tank while out there.
I have come across the jehmco option of having 2 500W heaters on their controller.