>I am looking for anybody who has built a sea kayak using marine plywood
>overlaid with fiberglass or epoxy.
I've built quite a few driftboats with plywood and (epoxy) fiberglass,
and I don't like it (that combination) much. I think (end grain)
balsa wood makes a better core material. The trouble with plywood is
the direction of the grain. Inevitably, the fiberglass covering gets
dinged, allowing moisture to penetrate to the core of the plywood.
And then it (the moisture) can travel sideways with the grain, forever.
I've seen small cuts in epoxy-fiberglass lead to water-saturated
bubbles 2' across, when plywood was used as the core material.
End grain balsa wood keeps any moisture trapped locally, however,
within an inch or two from any small dings in the skin.