We have two lids, one for the
freezer and one referigeration, that we made to seal rectangular openings the lids are about 1' wider at the perimeter than the hole with an insulated thicker center with a perimeter about 1/8" less than the opening all around. The lid seats with gravity upon a 1" wide rim of weatherstripping
sold in a roll from Home Depot. I took care to miter cut the ends of the seal and fit them well. We pry open the lids freely and frequently so far with little wear. We've had this design for ten years and I have replaced the weatherstripping twice due to wear. Take care and joy, Aythya crew