Marine Grade Plywood?
Actually, just thinking more about this: Since you seem to now be leaning toward a boat for gunkholing around lakes and rivers, you''ll want to find a way to make her bottom bullet-proof (hey, no laughing). From my days canoeing the rivers of the Midwest, I can attest that you will encounter any number of deadheads, rocks and other obstructions which will prove damaging or deadly to a plywood boat. Maybe there''s a way of sheathing in aluminum?? Something to think about anyway.