I'm building a Vacuum Kiln to dry wood. It is made out of 12" PVC Pipe -- See How to tap a large hole in a big PVC Pipe
I'm using the solid surface counter-top material Corian since it is not porous and it is relatively strong and a 1" thick slab will not deflect / fail (crack shatter) when under a vacuum. You can glue it together and the epoxy glue welds it so that it is strong as heck.
My first attempt at making an end for the kiln was a failure. I had to go back to the drawing board and learn how to use a new tool for the vertical mill --- the 360 degree table. It is so versatile, I wanted to do an instructable on it.