I made one for the 89 years ago and I made it from baltic birch plywood or some call it marine plywood. It is easy to work with and lighter than mdf and osb. It's available at any home improvement store. It's strength is that it's water resistant glued, multi plies and home built planes are often made out of it. I also painted it with gator gaurd bed liner and it turned out bitchin. I also ran a stringer down the middle on the under side and boxed around the edges about 3" up to add additional strength.
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