I went to the dealership and discovered that none of the GM capless fuel doors have a rubber gasket on the door. I saw photos on the internet of snow in the fuel filler tubes. bSo I think my fix will probably work fine. The other day, I had gone to Home Depot looking at caps in the plumbing dept. I found a flexible pipe cap that would fit over the filler tube and not interfere with the closing of the door. The size is 2 in. It is made of rubber. Remove the hose clamp from the cap and the cap will slide over the filler tube. It is not a loose fit. Slips of to fill gas then slips back on. GM engineers should have installed a rubber gasket on the door and it would seal the inlet or just kept the gas cap.