Tony G,
Thanks for your vote of confidence, Tony. The sub-sole fuel tank is indeed constructed of plywood with two layers of 3/4 oz matt and at least two coats of resin applied over the lot, sanding between coats. I didn't know you could do that either, but the word is, it works if you give the epoxy about 12 weeks to cure. Same with the water tanks. If you fill the tanks before the full cure, the water will be tainted with epoxy taste, but that clears after awhile.
All exposed plywood below decks will be veneered in Tasmanian oak, trimmed with teak and varnished. Some plywood with a decent grain, e.g. underside of doghouse roof, will be epoxied and then varnished.
As far as headroom goes, I didn't place much importance on it. I go below to sleep, eat & poo, all sit down jobs. I spend (or used to spend) most of my time in the cockpit, or the beer garden. My height is or was 5' 10-3/4", since I broke my legs, I am 5' 9-1/2" on my right leg and 5' 10-34" on my left leg. It seems the boat is always listing to port or starboard depending on whether I'm facing forward or aft