If GRP bulkhead use gelcoat filler applied with a small disposable syringe (less needle).
If wood, I drill out to clean hole then glue in a dowel sand, stain and varnish to match.
[/ QUOTE ] Sorry assumed it was wood. Yes the easiest way of filling holes in grp is to fill with ordinary plastic padding body filler until just below the surface then finish off with gel coat filler (Plastic padding do white) If necessary drill our a bit of the filler before doing the gel coat. Stick a bit of insulation tape on so that it cures non tacky and nice and smooth. Or gently rubdown to a nice level tack free surface. Brummer although the first "r" always seemed to be missing from the tins in the school woodwork shop.