Originally Posted by Mark
I like the concept but would probably go thicker. As long as you can compress it enough to fit inside.
As for insulation, its value comes from dead air space between the layers. Thermal eddy currents can form within this space; which lowers the insulation value. That why batting is used versus just dead air space. But some batting can absorb moisture (which acts as a conductor).
I think cutting up a couple of water heater jackets to fit would work pretty good.
All this being said, I only use wood, which is free. so I don't really care about efficiency. If I had to buy charcoal, I'd probably reconsider.
What is your reason for going thicker on the metal?