Key is don't make it more than it is.
This is how I would do it as an exterior repair.
1.) Prep the work area. Grind back the gell coat and feather the fibergall about 1/2 to 3/4 of and inch from the hole. (like the white hull posted above)
2.) Prepare your patch. Cut 3 or 4 layer of fiberglass to cover hole and exposed fiberglass. Cut 2 addtional layers that are the size of the hole only. (I preffer mat over cloth)
3.) Mix your resin. On a peice of cardboard lay out one of the larger layers. Pour the resin on it or use a brush to saturate the fiberglass. Add the second large layer and repeat with brush, then the third. Repeat with the small layers. Next use a paint stir stick and press the sandwich together. Your wanting to work out air bubbles and excess resin. FIBERGLASS HAS STRENGHT RESIN ONLY HOLD IT TOGETHER!!!
4.) Apply patch to boat. Brush a little resin onto the preped area of the hull to wet. Apply patch. use your stir stick to press the patch against the hull. Work out any excess resin and air bubbles. Next take strips of duct tape and streach across repair. This will keep the fiberglass in place while it cures and it will help it conform to the shape you want.
5,) Rough in the new patch. Remove the tape and sand down any high spots. Then add filler (fiberglass, Bondo or Adheasive) as need to restore shape.
6.) Sealer. I would spray a paint sealer on next. Sand lightly
7.) Finish with gell coat or get some really cool sticker to cover it up.
Grand Auto has diamond plate decals???
Hope this gives you some ideas.
If you want to do a internal / external repair send me an email. Corkguy1390 (at) SBCglobal.net