Hello Chuck- those of us who use CNC find any CNC experience is helpful. You well may know tricks the Bot community would love to learn.
I am curious why you would give up 5" Z height for a vacuum fixture?
I have made several small vacuum "sub tables" from HDPE or Plywood, and they are never more than 1" thick before the spoilboard.
I use Trupan for a spoilboard for vacuum, and MDF for mechanical hold down.
Jack is giving good advise on the MDF, its like window screen when it comes to solid. Not. Plywood can be air tight, get high quality non-chinese plywood. A coat of epoxy or other finish will guarantee it.
Good luck with both your health and your business.
D
"The best thing about building something new is either you succeed or learn something. Its a win-win situation."
--Greg Westbrook