I would use 1/4 inch marine grade plywood and have the wood fiberglassed before you install it in the boat. This will protect it and keep it sturdy,waterproof and light. I made the mistake once of putting 3/4 inch on the bow and it was sturdy all right, and waaaay too heavy too ! If you install wood anywhere, water and rotting is your enemy. The marine grade plywood is better but if you fiberglass it , then the life of it will last alot longer. I know if you carpet the wood and use carpet glue to hold down the carpet, the carpet glue will help protect the wood . I found that out myself. If I could do it over again though, I would have glassed some 1/4 inch. Also spend the extra money on true stainless steel hinges or use the plastic hatches / lids that are made to be walked on too. They seal alot better and will last longer. Sorry to ramble on but I have alot of useless information in my head.