I have used pvc to make a frame for covers for years. I buy the galvanized pipe holders and screw them to the sides of my beds with two screws. The pvc's springy nature puts tension on the clamps and they do not lift out in a wind.
Since I discovered hoop loops, I rarely use the PVC tubes any more. They are much easier to put in and their cost is about the same.
http://www.farmtek.com/farm/supplies...nnels;pg110239