If you are going to fill the holes with epoxy, then by all means use the West Six Ten product, it is much better than anything Lowes has on the shelf. It is VERY good for this purpose and easy to use - the caulking tube dispenser allows you to inject it deep into the holes without bubbles. It is thickened enough that it will not run out of the hole, even an overhead one. It will take at least overnight to harden to strength, 24 hours would be better. You can speed that up with some heat.
However epoxy at its best will not hold as well as the original wood and fiberglass. I personally would be reluctant to drill holes for dowels, these would necessarily have to be fairly large and through the fiberglass, exposing more wood to the elements.
I would attack it this way: Drill a very small hole through the existing pulled out screw locations to daylight on the other side - this is just to allow the air to escape as you inject it with the Six10 epoxy. A very small hole (say 1/16) will allow the air to escape but not much epoxy, too thick. That will allow you to completely will the holes with Six10. I would then drill a couple of additional holes in the bracket at the top and the bottom in new locations and add those screws when I reinstalled. These will be into fresh original material, and after all it is the couple of screws at the top and bottom that are doing most of the work. The result would be indistinguishable in appearance from the original.
