A couple of weeks ago I got some 3'x8' sheets of plywood off Craig's list for free from a church's festival who decided their day was over. My guess, based on the plywood cores, is that they were made some time in the '80s. Anyway, snatched it up and it's 1/2" painted plywood with lots of sticky Velcro and hot glue on one side. Had to add some 3/4" CDX plywood from the scrap bin waiting-for-the-right-project pile for the torsion boxes.
Velcro goes on the non-show surface. I need to get a bit more hardware, then do some alignment and attach the supports. I also have to make a dust hood for the back. Re-purposed those sheets just fine.
Re-