I'd expect the miter joints to be caulked with a typical 1/8" or 1/4" or so margin of caulk same as surrounding. As you well know all wood moves more longitudinally than laterally and that's true even on epoxy unless...perhaps...the mitered joint has a spline or two installed to greatly increase the gluing area of the miter. I mean, caulk is all about taking up movement in the wood and being adhered to the wood to protect it. That's the trouble with living, breathing boats and houses and stuff, ain't it? Heh.

Thinning all that wood down to a place wherein the epoxy is stronger than the wood movement is what cold molding is all about to begin with and the thicker the wood from that base of controlled movement, the more problematic the control of moisture, i.e. movement, which is the nemesis of all boats. Why, oh why, do we then take our beautiful creations, these works of art over which we slave lo these many years, and insert them into the very water we want to keep out, allow rain and snow and sleet to fall upon our art...........but I digress.