Well
I'd use acryic/plexiglass. You could even "hinge" it using something as simple as an 1/8" drill bit and waxed thread/ fishing line. I have some extra plastic "spacers" (the things hat slip on to the back of the glass tops that you cut to fit around the filters, etc.) I'd be willing to donate to your endeavor although you could cut your back sections to fit whatever set-up you want and not need such. If you go this route just get some sheeting that's thick enough that it doesn't bow in on itself.