It seems to me there is some confusion here. The hull, for practical purposes, has two portions. The part above the waterline and the part below the waterline. Below the waterline, an antifouling paint is applied to keep fouling of algae, grass and mussels and barnacles, etc. depending on where you sail. To prevent blisters, or to repair blisters below the waterline is when one would use an epoxy water barrier coat between the hull fiberglass and the antifouling paint. You mention you have no blisters, but your cast iron keep is rusting. That needs to be cleaned as best as you can and primed with a primer designed for steel. Then, if you need to do any fairing to make it smooth, you trowel on some epoxy fairing compound . Then apply antifouling paint of your choice.. Which paint? That is another topic cover already by me and others so you can search for that or ask.
Above the waterline the boat has bare gel coat, which was applied inside the hull as the first step in laminating the hull with fiberglass. That, along with the shear and waterline stripes are gelcoat. After being exposed to the sun, the gelcoat can oxidize and become dull. The first thing to try is buffing it out with a power buffer and a gelcoat rubbing compound. That hopefully brings the hull back to a shine in which case you would apply a good wax for the sun to chew on rather than your gelcoat. If your hull is so oxidized so that buffing it out does not bring up a shine, you can carefully wet sand the hull thoroughly and then buff out the hull. This is very intensive work. If that doesn't do the trick, then repainting is the next best solution. There are DIY paint formulations for the boat owner, or you can hire it done by a professional.
Good luck.
