Ron, the prints are pretty flat to begin with. I even tried sheets, rather than cuts from rolls. The poster hangers I got clamped the print with a kind of cam action. No matter how carefully I closed the hanger, it distorted the sheet, causing the ripples.
John, your system looks like it has great potential. Your images show an excellent presentation, far nicer than my result.
Can you show how they hang on the wall? I don't see the topside hanger wires that others (and me) didn't like.
Also, I don't see how the roofing nails come in to play. Can you photograph that part?