Before you but the bases back on, take a countersink to the holes in the
gelcoat. The space gives the
sealant a place to go instead of squeezing out - kind of like putting a small o-ring on the fastener shaft. And make sure you check the deck
core - if there's any doubt, rip out the
core and fill it in with kitty hair (epoxy with
fiberglass strands mixed in). You don't want to lean up against it in
weather and feel too much flex - makes you religious in a hurry...