I did a little searching for a hoop rack and found a few references to them. Some people seem to use clothing racks and I found at least one example of a PVC rack that someone had made. My handy husband and I were able to come up with a similar design for a PVC hula hoop display rack.
Together we figured out how many connectors we would need as well as how much PVC tubing (50'). We decided on 3/4" PVC with the thicker inner wall. The project didn't cost too much to make and took an evening to cut and assemble. My husband used a hand saw and we didn't end up gluing it together. The measurements were based on hoop sizes for the width. The height of various parts were decided based on testing with hoops.
The rack seems to work very well for my hoops. I decided to remove the PVC lettering with acetone and decorate the rack with my business name and gaffer tape.
After it was made, I measured my mini van and the rack width and height. Fortunately, it will fit assembled! That might have been a good consideration when designing the rack. The rack width is 42.5" and the height is about 41" and the length is 47.5".