Norman, another possibility is to make your bed in a couple of pieces rather than one, with flanges that bolt together. The flanges will actually help stiffness and act as webs. If it's anything like the Gingery, it will scraped (or milled) after, and then be covered with a full length slab of cold rolled steel anyway. It will easily be as strong and stiff as a full length bed, and the molding, melting and casting will all be easier.