Butyl rubber tape, white. I buy a roll of tape that is about 3/4” wide by 1/8” thick. Zero leaks and I use it for almost everything topside. Just put in a new anchor windless on my 26. The windless and the anchor locker door have been bedded with butyl rubber. Some fool previously used silicone caulk and didn’t take the time to seal the balsa core. The core of the anchor locker door area and the windless are now sealed with epoxy.
Tech tip: when working on a specific area doing bedding or epoxy work, tape a plastic grocery bag next to your work area to place all of your waste in. Working on a hatch or fitting, place blue painters tape around the perimeter of the object. If using epoxy use good quality duct tape below the work area (epoxy doesn’t stick to the tape as long as you remove it, before the epoxy fully cures). Bed your hatch or whatever with butyl rubber tape. Bolt the item down, carefully score the item with a putty knife edge, remove the blue tape and you are done.