What method are you using? Rope? Screwdrivers/putty knife? I use the rope method with the ends at the bottom. Get a strong but reasonably small diameter nylon rope. I generally install the gasket on the glass (no sealer), plant the bottom edge in the pinch weld, and then start pulling on the rope toward each lower corner making sure the gasket is seated properly. Carefully work the rope around each lower corner and start working evenly up the sides. It helps if you have an assistant to keep some slight inward pressure on the glass. Keep working your way up the sides and around the top corners working both sides equally. The last bit in the middle of the top should be easy. Finally, tap on the outside of the glass with a bare palm of your hand (no rings or other metal!) to make sure it's seated all the way in. As long as the glass is clean, a new gasket, and the pinch weld is in good shape, you shouldn't need a sealer. If the pinch weld is sketchy, use some non-hardening sealer in the pinch weld groove in the gasket before installation. Makes kind of a mess with the rope in there, but, better than trying to keep it on the pinch weld during installation. I you don't use a sealer, I like using liquid soap or some gritless hand cleaner (GoJo) to lube the rope and rubber to the installation process. I use a little WD40 if I use a sealer....tends to soften the sealer a bit, but, also helps you pull the rope out.