pic: 3/4" Plywood Frame

[Bertman]

We have made several plywood frames over the years. If you use 3/8" plywood (I would use Baltic Birch which has at least 5 layers and no voids) as a top with a 1/4" Baltic Birch Ply bottom - sandwiching 1/2" -3/4" X 3/4" spacers around the perimeter, all glued and clamped, with solid blocks at mounting points for pillow blocks and super-structures you will create a hollow chassis which is light and incredibly strong and stiff. For inspiration look to light wieght, wooden boat construction. Go for it and good luck.