RB writes:

Seems we used to use glazing putty to stopper holes in the boat where we
took stuff off. Maybe so, maybe not---my memory isn't good anymore.
Anyway, would glazing putty be a good filler for that kind of use?

Glazing putty is an ancient compound consisting of linseed oil and ground
rock. It is a good filler if squeezing seeds and grinding rocks is the
level of your technology. Otherwise, you may want to consider modern
things like epoxy, polyurethane, or polyester.