like shape it to a curve so it will stay with out being attached to something? i believe there is some sort of clamps/form/steam thing you can do, but that shouldn't be needed for a curved rail. you should be able to find a way to make a curved frame by cutting the wood the right way, and plywood/pvc should be able to stay shaped to a curve if its not to thick, the curve is not to sharp, and you attach it somehow.