Looks like somebody responded with a technique to patch the fiberglass pieces together.
Just to expand on that a little .. the gelcoat is what they use to pick up the fine details of the mold they used to make the fiberglass piece. Its the first layer they put down before they put in the reinforced mat and resin. The resin sticks to it pretty good. So often times when you have a fiberglass piece with a gelcoat, it may be necessary to lay down a skim coat of fine body filler to get a really nice and smooth finish.
So as far as what you're doing, as long as you lay down the mat in the back for reinforcement, and then use a little mat or resin to fill the pieces, you should be fine as long as you sand it all down even. You'll probably need to use the body filler either way to make it all blend together if you have any kind of bubbles or anything else in your resin.
Just my .02
- Dan