It's a simple wooden tray and a couple uprights with rounded top and bottom ends. Surrounding the tray and uprights is a piece of 8"-dia. duct tube that's been separated along its crimped seam and spread open over the uprights. Neat.
Complete plans are in Autumn GardenScapes. You can get a copy at your local newsstand, or visit GardenGateStore.com to see more of what's in the new 100-page softcover book.