my experience is in the marine environment
gelcoat is not actually waterproof...
water will still get in the glass but at such a slow rate that it should not be a concern for you (pb for me though, it can add hundreds to thousands of pounds to a boat hull)
it can be done
but i have only done it using a mold and small repair work (
where i start with a fiberglass gelcoated mold
apply a nonstick coating, gelcoat, chop, then the fiberglass matting and resin
the number of layers of matting depends on boat size and use
chop is inch long bits of glass sprayed simultaneously with resin and it prevents the matting from showing though the gelcoat (because of the randomness of the spray it produces a much smoother surface
for your application, i have little experience. i'm pretty sure doing matting in sections will be not a pb, however be sure to leave an overlap of matting
a foot or so of matting with out resin with which you can lock in the next section
you can skip the chop, it is not structurally necessary, but produces a more ascetically pleasing product
each coat of gelcoat should be done in one shot and best results come from spraying it on
where in MI are you from? Saugatuck, MI has the Broward Boat Building plant (maybe, may have closed
) they might be able to help, however i think a lot of their work was in AL so don't kill yourself finding them. they build megayachts