One good technique for making fiberglass stick, is to drill little holes in the surface, lets the resin leak through and get a grip on it. Or, you could lay a single layer down, then drill and pop some pop rivets ( after it dries ) then you can add more layers till your depth is achieved. Even if the first layer separates, the pop rivets will hold it all together.

Whatever you use, you will have better luck if you rough up the surface first, with maybe a bondo file or 60 grit paper. Then, wash it down with laquer thinner.

good luck