Based on the truck pics that post for each of your signatures, I can't imagine having too much trouble with glassing--I mean, you obviously know how to wrench a bit and you wouldn't own one of these trucks unless you had a pretty large set! Be nice if all you had was minor league repairs to practice on, but Fun in the Dirt's going right to the big leagues based on his pics.
The biggest thing to keep in mind is that it is a process, and the materials really won't let you skip steps or go too fast. You'll see bubbles or sags as soon as it catalyzes. You can pay dearly for trying to shortcut a step in the sense that you'll get to start all over, but that's about it.
Fun in the Dirt: fiberglass adheres to about anything, so clean up the nasty gram that the PO left you, stuff something solid in there and maybe put a few screws into the repair from the inside and outside of the top to hold everything in place. For that matter, you could fit a piece of wood to fit inside the bottom lid of the hatch, stick some epoxy/ JB Weld on the inside of the repair and stuff the wood in the hole. Regardless of how you hold it place, it then just becomes cosmetic repair. Multiple layers and larger and larger mats.
As far as strength, this'll either reassure you or just make you roll you eyes: one of my shop specialties was was putting old surfboards back together...as in, they were busted completely in half. This was for older boards, ones with sentimental value where additional weight wasn't any big deal. We would put make 5-6 holes on each half of the foam part of the board by pushing a pencil in the foam. We'd mix up a batch of resin with a fiberglass base to form a paste, stuff it in the holes and along the entire surface of the exposed foam. We'd push the two halves together and clamp it as best we could and let it go off. We'd cut a mat for the top of the board to cover the repair and then some, glass it, flip the board, glass the bottom of the repair, mat and glass the sides of the repair. The key was overlapping the various mats and extending them well beyond the actual repair. We'd sand the edges of the repair, gloss coat it and sand and polish that.
There are guys still using boards we repaired years ago. I can't see a top repair having more strain than a surfboard--unless you're upside down, a whole different issue!
I'll probably tackle my top this weekend--I have to glass a bunch of baseball bats for the local sporting goods store, so I might as well make up a big batch and get after everything at once.
I think I'll glass the cat as well
