I have built my icebox using 4" of PolyISO insulation with has an R-value of 12.9 per 2" according to the manufacturer. This will be accessible from the countertop in a side by side freezer/fridge design. I am hoping to have a freezer system with a spillover fridge. I am working with a company to provide a condenser with a coldplate for the freezer. There'll be two fans in the separation wall that will be controlled by a thermostat in the fridge.
The inside of the icebox is lined with 1/4" marine plywood and covered with 6oz fiberglass cloth using West Systems epoxy resin. I plan to apply white gel coat tomorrow.
Dream it. Design it. Build it. A hobbyist at heart, I'm usually asked, "Wouldn't it be cheaper and easier to just buy that?!?". Sure, but then I wouldn't understand it and appreciate it like only a do-it-your-selfer can!