I never went through with the purchase at that time. I ended up canceling the order
I bought a couple of foam board sheets and sandwiched the posters between the boards. But there ended up being too many posters so even the foamboard sandwich couldn't hold with the clamps.
I then purchased poly bags from uline. But they need backing boards to flip through the posters.
Sounds like the way to proceed, Mike. Smooth backing boards and the poly bags. A good combo and the posters can be flipped thru, too.