Vitamaltz's approach works good.
Just a thought along those lines: if you rig up some sort of top post ( like a metal ridgeline ), you won't need much at all to hold the uprights, mm, upright. I hung from 2x4s for 2 years, and it never flexed even a fraction of an inch as far as I could tell. All the rest of the heavy wooden stand really only served to hold the 2x4s vertical. Without the top bar, it would have collapsed quickly when weighted. I could flex it pretty good just by pulling on it hard, without the top post(spreader bar? top bar? don't kmow what to call it). I had two pieces of fence top post about, I think, 14 feet long total. Then I had about a 5 foot piece of slightly larger diameter fence "upright?". again don't remember what it is called. The fence post that goes in the ground. The longer ones went inside this, to keep it from flexing at the joint. Then I drilled some holes about 1/2" deep in the 2x4s just wide enough for the fence post to fit in. It was bombproof. Even after a couple of years with untreated wood, which was looking really questionable, it was still solid. The fence post took virtually 100% of the load.
I'm not sure how you would rig that up on metal uprights, but I'm sure it could be done. Just an alternative route.