Currently one side of the plastic has brass grommets installed through the end of the plastic that has been folded over itself 4-5 times giving it a thicker seam. The grommets hook to simple screws that are in the outside of the boards sticking out an inch. I tried using grommets on both sides but I found that the stress each day pulling it to cover/un-cover/hook, the grommets pulled out. So now I just use the grommets on one side and the spring clamps you see in the picture on the other side. This makes it very easy to pull back each day and it has weathered some pretty serious wind as well.
I don't have closeup pictures with me but will post some tonight.