Epoxy usually cures over polyester/vinylester, but poly/vinylester gel coat doesn't cure over epoxy. I went with B Hogan's advice and ordered the Evercoat stuff - epoxy seems to degrade in UV more than polyester, and it's always good to stick with the same materials (pun). There's a big void in thick gel coat where the skeg slider slides. Has sharp edges that cut my thumb (boo hoo). Only part of the bubble has worn through, so will be interesting to see how big the bubble actually is when I attack it with a Dremel - another reason why I went with the Evercoat, which claims to be a paste and might be thicker than standard gel coat, so easier to use here. This job will require removal of the slider/cable.