installing Weaver snap davits on swim platform

[funinthesun]

I'm going to install the Weaver snap davits on my fiberglass swim platform. There are already indentations for them, all I have to do is drill the holes and install the snaps. My question is regarding sealing the holes I drilled. After I drill the holes, I'm guessing I should fill them up with some sealant. Which sealant, and how much?
Thanks,
Ed