I used marine 3/8" plywood under the Corian in my galley. Before I wised-up and canned the garbage grade RV fittings for marine the wood got flooded. So did the deck. After it dried (3 or 5 accidents) I looked at stuff through a magnifying glass and there is not a speck of evidence of getting wet. This was some 20 years ago so if there was going to be dry rot it would have happened. I wish I could have got it at a real deal price like the Teak but had to pay full bore. Ship's chandleries know where to get authentic marine plywood. I had John the ship's carpenter spray marine varnish over the wood. That bus will get passed down to my grandkids. The skin is 16 gauge hot dipped galvanized 1013 steel. Look for that certification number applied to both sides of each sheet. And GOB marine varnish onto all edges. This helps seal the lamination. Good luck.