I've never been that keen on the idea of epoxying a grp hull.
There's the argument that the epoxy barrier is equally permeable in both directions and any damage to the epoxy would allow water in and keep it there. Then, if your hull is not new (in my case nearly 37yo) and has shown no signs of osmosis yet, why would you bother?
There's lots of other stuff to spend money on.
And indeed that was where I finished up.
My original thinking was that since my hull consists of two fairly thin layers of GRP sandwiching the foam it might be worthwhile adding a protective layer. Some years later, when cutting a hole for my FLS, I discovered that at least the bottom part of the hull is solid GRP about 30mm thick which was greatly reassuring! I haven't established at what point the transition from solid to sandwich construction occurs (I might try some experiments with a joist finder) but if it is below the waterline then there might be an argument for applying a belt of epoxy to that part only, leaving the solid GRP alone.
OTOH I may just go sailing!