Do ski boxes made with plastic or other smooth materials tops need coping on the sides?

I have a frame and box built and might put Plexigl or something on top instead of PVC piping like lots of people have suggested. I don't know if anyone has just put Plexigl on it without a PVC or metal coping. do you think i need coping and what should i use for the top material, Plexiglas or something else. PLZ HLP