: You're correct, this plywood would fall to pieces if exposed to water. It was
: considerably cheaper and a 1/4" thicker. I'll probably make up the
: cost in sealing it properly.

Having recently read the West System manual, they mention that thinning the epoxy also reduces it's beneficial properties, so it's probably best to use it straight. On Tom's site, he mentions that he coats bulkheads with one over-all coat, with an additional coat on the exposed edges, with varnish afterwards. And that's on marine ply, so I think you may need to do some extra coats on the interior birch ply.