I converted my ice box in January. I was lucky that the PO framed in the original ice box and filled the void with expanding foam. All I had to do was add rigid foam to the top (bottom of the counter top). I also added a gasket system. The lid gasket and plugging the drain was critical in keeping moisture out and the plates from frosting over.
Make sure you purchase a system appropriate for the cubic feet of the box. I don't have a real need for a "freezer" I can put frozen items next to the plate and it will keep kind of frozen for 4-5 days. I put drink ice in a zip lock bag and into a insulated lunch box bag and leave it in the fridge and it stays frozen just fine.
