In my former life as a sailboat Captain [ that mean's I paid the bill for
the loan ] I never had to replace, rebed, or reattache, or put on new
........... hardware. Things such as cleats, winches, etc.

Could someone tell me the correct way to go about doing this with a
fiberglass boat.

Say, a cleat. I understand that there must be a screw, or whatever that
goes into the deck to hold the cleat in place,,,,, what about sealing the
deck. And, on the inside of the deck [ below ] is there a backing plate
that the fastener of the cleat goes down through? What type of bedding is
proper.

Just a quick go through.

Thanks ,,,