Center the sheet metal over the wood and drill 4 holes,
one in each corner. Put a screw in each corner. I used
Phillips Mod Truss, Lath, Self Drill screws that are 1 1/4
inches long. Don't screw in the screws all the way yet.
Take a rubber mallet and pound the sheet metal to wrap
around the sides of the plywood. You will have to snip
the corners with tin snips. Underneath the plywood,
glue two rails along the sides, laying the wider sides
flat to reach from corner to corner. I used 1 inch by
2 inch MDF fiberboard. Pre-drill holes in the MDF for
the screws because the fiberboard splits. Now screw the
4 screws all the way into the rails. You wil build 5 of
these panels. All the rails run horizontally (left to right)
with the wider 2 inch side lying flat.
Because the MDF splits easily,
I would use
some other 1 inch by 2 inch rail, something
cheap like pine.