pic: 3/4" Plywood Frame

[DonRotolo]

There are many grades of plywood; you want aircraft plywood if possible. It uses many layers of light wood.

regular plywood, like used for house construction, uses only a few layers, and is not as strong (or light) as aircraft plywood. Marine plywood uses a few more layers, but isn't as light. You might consider making your own plywood, two 1/4" aircraft ply outer layers with foam and 1/4" spacers in-between - lighter and just as strong.

For stiffness, use pieces mounted 90 degrees to the plane - glue and screw.

It would be heavier than aluminum, but plenty strong. Use some aluminum U channel along the outer edge to give very good impact strength.

But nice concept!

[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.