I stopped my anchor hatch from rattling and leaking by using "cap seal"-the sealing tape used to install truck caps. Cap seal comes in a roll of 12 or 24 feet and is about 2" wide and a 1/4" thick and has adhesive on one side. To install the seal, first clean and dry the area around the edge of the hatch. Cut it and dry-fit the seal first, then peel off the backing, section by section, and press it into place around the hatch. It may be tight at first, but it will compress over time.