Took trailer to repair shop, dang i wish i would have sat down... $2000 min in repair work, yup I'll step up and do the work.
I'll not claim "expert" regarding the skill required for repair either. However, one of my (too many) careers was in selling equipment, tooling, and supplies to manufacturers of such products. Depending on volume, these trailers were probably built with the outer shell being done in a mold. In the process, the mold is meticulously cleaned, polished, and kept free of contamination. At least, the outer shell is formed in the mold possibly using a fine layer of non-woven fiber & resin. Additional layers could be applied for strength.
I had one customer who used a process called Reactive Injection Molding. That is where the mold was sprayed with the finish coat by a spray gun, and then the mold was closed, the liquified substrate (molten plastic) was pumped in, cured under controlled heating, and after a set time, the mold was separated, to reveal a shiny finished tractor fender. In this case, it was not fiberglass, but some kind of thermoset plastic compound.
This trailer looks much like it was built in a process similar to boat hull manufacturing. Repairing it will be similar to the challenges of repairing a damaged boat hull. If you have or know of a marine repair or supply shop, perhaps you can get some good advice, and purchase a kit to do the repair yourself. Key will be to follow the instructions, get the glass substrate properly prepped, matting wet, layered in without air bubbles, and within "set-up" time of the resin. In addition to the chemical ratios of the resin/catalyst, fiberglass tends to have an overall "cure" time that must be allowed to run its course before final finishing. If you try to finish it too soon, a shrinkage line could form in the repair area. Follow the instructions, and it should do fine.
If you are an incurable tinkerer (like me), the repair itself could become an enjoyable adventure in itself. Sometimes, "the story" of a project is more important than "perfection." If you are a perfectionist...then this could be miserable drudgery, and perhaps better left for a professional.