I have had these cracks repaired at the factory. During the repairs I checked in at the factory daily since I wanted to see what was being done.
This is not simply a fiberglass repair, and I would not trust this to any RV repair guys. For the repair they removed the fiberglass skin in a large area. They then welded additional aluminum supports into the wall. Then they had to replace the fiberglass skin, get it to match the existing fiberglass and replace any decals that may have been damaged in the process. The repair guys at the factory have the know-how and the means to do this work. (On one of the cracks I had they had to remove the front cap, well beyond the scope of most RV repair places.) Simply patching the fiberglass will only result in the cracks coming back.
Finally, and this is an added bonus of going to the factory, they go over a lot of items on your rig and make any needed repairs. They repaired a lot of items on my rig that I was not aware of. The guys doing the work are super nice and willing to explain what is going on. It's a bit concerning initially when you walk in and see your rig torn apart, but after having them do this work I can say that taking it anywhere else would be a huge mistake. Also, from having been to the factory twice - the repair process is substantially improved from a couple of years ago,