The ice box was way too big. It turned out to be nearly twice a big as I thought divided by a pair of one inch foam sheets cut to fit. The aft half was only barely accessible from a hatch in the cockpit. The last photo is from inside the cabin looking into the ice cavern with the teak gratings and insulating foam divider removed.

Reducing the size of the ice box is now a job for the reciprocating saw (aka sawzall) and some fiberglass work. This will make room to the side of the engine compartment that can house the refrigeration system, any water maker added later, the charge controllers and the AC charger.