i dont believe his garage is insulated. just the garage under the house, foundations, concrete, thats the problem i believe.
the only way to do it is to line the tank as lining the garage would be difficult, though i would do it, but will cost a bit to line with poly.
in saying that, i lined my garage with poly costing 400 dollars, the power it saves me was returned in less than 4 months. power bill went down fast, temperature held better.
Poly on glass is my suggestion.