I just read in a thread where these are not viewed in a favorable light. Look for posting #30 to see what I mean. I removed mine 10 minutes after I power it up for the first time.
If you are talking about using it like a vacuum table, any opening around the work material will will pretty much kill the vacuum effect. Read this in another posting too.
If you are placing the laser on a workbench, I think a canvas cover over a PVC pipe frame would work great, and not be too heavy. You can get Red transparent 1/16" plexiglass fairly cheap for viewing ports.