....a seam-filling project.

It's been a long time since I have worked on a wood boat, so long that
even if I could remember what I used to fill seams and then paint them,
I'm sure it no longer would be available.

So, here's what we have...a seam between two planks on a deck. I want to
fill the seam with some sort of material that will dry to a fairly
smooth, sandable surface, be waterproof, and be paintable.

Plastic Wood? Anything better? I remember some "Petit" brand products
from 50 years ago, but I doubt they're still manufactured.

?