I've seen some made from 8" PVC pipe. Maybe some scrap sections and cutoffs would work? If you can visit a Pipe yard or a construction site they would likely give you the 2' sections they cut off?

I know I had a need for some 5' sections, for another project. It took a while but I had the irrigation company here give me two pieces and I paid like 25 bucks for the third one. They would be far more weatherproof too!

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