The inside of a grp boat is usually quite rough. I know mine is.
Options are limited, I have considered a thickened epoxy and sanding it smooth, but the dust!!
I have considered thick paint to try and fill the hollows, and I will probably end up with bilge paint on the hull and some form of cladding over the top. Either a foam or thin ply where the elbows and knees are likely to find the hull.
If you come up with anything else please share.
🙂