Although not a GTO, I bought one from OPGI for my ElCo several years ago. It was on sale, fit well, four layers, and no markings beyond a small 'FRONT' tag. I use it in the garage to keep the dust and other things off and space in my garage is tight, so it helps prevent those minor dings and scratches that may occur. Since the bed is next to the garage refrigerator I also use harbor freight moving blankets over the rear fenders if someone opens the refrigerator door too wide.
https://www.opgi.com/car-care-paint/...p-gch727l.html