For those of you still looking to make one of these frames, check out this link I read about on a longarm forum I'm in, for the Snap Clamps. They are available in different sizes so you could easily purchase 1/4" larger than your pipe size, and you have a choice on the legnth as well. They also have all kinds of elbow fittings, Y fittings, etc.
http://www.littlegreenhouse.com/accessory/pvc.shtml
Hope this helps. :D