Several years ago I fabricated a set of blocks from sheets of 1/2-inch
rubber which I glued together to the appropriate thickness.  Once they
were glued together I cut them to size and shape on the band saw and
then drilled the holes through them on the drill press.  Since they are
held in place by the V shaped clips I was not worried about the glue
joint failing.

I got the rubber as scrap from an industrial rubber and hose supply
firm in Oklahoma City where I was living at the time.

Norman Cantrell