One approach is to bed the fitting with adhesive or sealant (on the outside and on the walls of the hole, slide the fitting in and tighten until you see the sealant ooze out completely around the outside fitting edge. Do not completely tighten yet. Wait a while, maybe 10 minutes for a sealant and longer for adhesives like 5200 ( slow cure 5200 can take a week to cure!). Then tighten the fitting. If the hull is solid glass where the hole is, you can tighten quite hard, If however the hull is cored ( for Grady's that is above the water line), don't overtighten . that can cause the walls of the hull to crush/deform