Mike,
I have seen boats less than a season old develop cracks in the deck like that .
The grain of the ply seperates a little and lets some moisture in. It happens more easily on decks with smaller radius camber.
This has happened even when treated with epoxy or evedure.

In my experience building a variety of 16 ft cats I have found that a light layer of plain weave glass ie between 90 and 135 grams makes this problem go away for the life
of the boat.
If you use 86gm per m2 plain weave glass and can wet it out with a resin glass ratio of 1:1 you should add something like 400gms to the total weight of your boat.
This will significantly reduce maintenace by eliminating this problem.

Just something to think about.

Regards,
Phill

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!