Bedding caulk
I use Boat Life 'Life Seal' for most bedding/sealing on my boat. It's a polyurethane-silicone mix, w/ mostly poly. Supposed to be good for 10 years. The slight amount of silicone in it makes it easy to remove the hardware later. 3M 5200 is an all-polyurethane that is best for bonding/sealing (like hull-to-deck joints). 4200 is a *less strong* 5200. Pretty good for most bedding jobs. 3M 101 is a polysulfide (like Life Calk), which is very good for wood-to-fiberglass sealing and general bedding jobs. Not for use with ABS/polycarbonate plastic (like Beckson deck plates), though. Life Seal works very well on plastic ports and deck plates.