Hey, Dale, my only concern with the posted design is whether the plastic is secured with rocks enough to avoid the wind tearing off the plastic. It is hard to see in the photos how you "tucked the plastic into the rocks". You probably did such a good job it won't be a problem, but I can't tell from the pics. The wind can put a large force on the plastic, so it needs to be anchored well.
The plastic wrap on my design is both anchored to the pipe with "snap clamps" and weighted down at all the edges with lots of concrete blocks. I don't see the snap clamp on yours, maybe they won't be needed.
Your koiphen chemist and environmental scientist.