Installing Refrigeration on my 27

I will be installing refrigeration on my 27 this week and am concerned about the insulation. Not so much around the outside of the existing ice box (as I understand that there is adequate insulation around it and I will add a little extra) but the lid itself. My 1974 just has a 1/4 inch lid that drops into a little lip on the countertop and is flush with the counter. This is obviously in adequate for good insulation. Has anyone out there re-modded their lid for this and how. So far I plan on gluing on a 2 inch piece of insulation type foam on the underside but I'm more concerned with the edges and keeping a tight seal between the lid and the lip and if possible still keeping the lid flush with the countertop.