Repairing fiberglass is one of the easier repairs to do at home. You can get good, high quality, glass, resin, etc at places like West Marine. A lot of the auto parts store kits are not very good.
It looks like you have room on the inside of the parts for extra thickness, so you are in good shape. The biggest mistake people make is trying to fit the parts back together as the came apart. I can almost guarantee that to be impossible because of the glass ends all over the place. You need to sand it back until you have a very small gap, near zero, between the parts. I like to take some thin aluminum strips and pop rivet them onto the loose piece and the matching piece to hold the repair together while you work on it. If you can get the strip on the back side, they can stay there forever if you want. If not you just remove them once you have it held in place with glass. The aluminum strips allow you to bend and move them around to get the right position. Fixing a bolt hole is also easy. Pop rivet a piece of aluminum on the inside and glass over it, drill out the rivets on the outside, and smooth the outside with resin or bondo, redrill the hole.
Here is a thread on another topic that shows how I repaired and altered the fiberglass ground affects on our Roadtrek. The repair would be similar to what you need, but the alterations were much more than you have to deal with on yours.