The best coating is a marine two-pack varnish. This contains the necessary UV protection for the carbon and epoxy underneath along with excellent abrasion resistance. SP Ultravar 2000 is a good choice.
As a second choice a marine 1-pack polyurethane varnish.
There is a world of difference between marine and domestic coatings - I did my south-facing windows with marine paint 15 years ago and they still don't need re-doing!