I looked at the Johnston Plastic website but did not see the HDPE. Then again, my "plastic" knowledge is severely limited.
I also noticed that you're using a Craftsman router. I'm scratch building a 24" X 36" and plan to use the Canadian Tire 11A 2HP Mastercraft Maximum plunge router that was on sale not too long ago. Making slow progress....
Did you document your build on the CNCZONE?