ANY decent epoxy , mixed with :
West-Systems 404 High-density adhesive filler ; will do
the job.

Do NOT use just any filler,(like micro-balloons) because
they are hollow spears that will break down with time.Some
fillers were designed as a sanding/fairing compound, and won't
work for a structural application !!

The splice i made for my Hobie-21se, i actually installed grease-nipples, and pumped in the filler with a grease-gun
from Harbor freight; then removed the nipples after the epoxy
gelled-off, but before it cured.
It worked Great !!

Bille