Take a box 1/2 insulation @ R-60 and the other half insulation at R-0. Effective insulation is R-30. Not "0". So where ever you end up with better R value you end up using less energy. Rparts had Vacuum panels at a good price. Assuming they still do. They're to last 10 years and at the end of their life simply be R-5 / panel. If you put the panels in side your box you reduce the area of the box and reduce the energy consumption too.

Try this site for playing with how much insulation will do what! http://www.glacierbay.com/Heatload_calculator/heatload.htm

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