Saw and Drill the Wood Fig. Remove the wood and lay it on a flat surface. Saw along these lines. It is not critical that the cuts be exactly straight, so an unguided hand-saw can do for the cutting. Drill appropriate width holes at the centers of the marked slots.
Test mount the tray on top of the spreaders.
Look through the drilled holes and make sure they line up with the spreader holes. Put a washer on each bolt and set them through the drilled holes. If the fit is tight, or the bolt holes don't line up, file down the wood corners. Raised sides may be added if you fear objects will roll off the tray. You can glue or nail thin strip of wood along the sides.