Gatorboard or Gatorfoam is available in lots of different sizes, plus three colors. I usually get mine from this company as they package it for shipping very, very well.
http://www.foamboardsource.com...oams--gatorfoam.html
It's very tough, but requires patience to cut it.
JohnS: The auger bit works perfect. I just turned the bit by hand enough to penetrate half of the Gatorboard on each side. Then a perfect hole was the result. Thanks much.
George (G3)