I forgot one thing. Where the hull joins the deck inside the hull, the glue often forms bubbles on the inside. Look closely, and carefully run your finger/thumb along that seam, you will see/feel the unevenness. Take a Dremel tool, or customize a sanding block, and sand down these bumps or bubbles, so that the transition between hull and deck is a gentle and consistent curve. This way, all glass reinforcing will adhere evenly all across that area where you are strengthening. Then those forces that can cause problems can transition, and won't 'go snap' in the middle where the glass will be unsupported.
For glass work, find others who are good at it, and buy them lots of beers. Practice on your own on some junk stuff. The best I know of is the WEST system, not cheap, but cleverly thought out. One pump from the large (resin) can to one pump for the small (hardener) can. Find out which is the best 'filler' to add, often 403 or 404, microballoons.
Learn the 'butterfly' method of laying down some plastic sheeting, (vapour barrier works well,) place the glass cloth on top, in the size that is handy to work with, wet it well with thoroughly mixed resin, cut around the plastic 1/2" or 1" outside of the cloth, pick up the whole thing, put the patch in place, use a small roller (on the plastic surface) to roll out all the air, then gentle peel off the plastic. Takes a bit of practice. Work slowly.
Don't be scared to take the H18 apart, and rotate the hulls as required so that excess resin can soak down into the seam. Gravity is wonderful.
You may find it easier to use 'seam tape' in 2" increments, that is 2" or 4" or 6" tape. Overlap the tape as required. Any good fibreglass shop or sailing store or high end hardware store will carry what you need. Or google WEST on the net. Check with your dealer or nearest sailing club.
1989 Hobie SX18 Sail # 1947 "In Theory..."
'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'