Nice job Steve!
The original design by Erik Wilcox called for the tubular trim off decorative garden edging as the ring material. However, this is expensive stuff to buy for the amount needed. It also requires more work as you need to cut the tube from the edging. The tubing is rather more rigid with a thicker wall than the poly pipe. However, the poly pipe is cheap, easier to work with and more than adequate for the job.
Mark