I never got around to it, but I was going to use a single square arch with crossmembers, using the Roll Control system.
Plan was to use a single hoop of about 1" or 1.5" SS tube bent to the height desired (just shy of the height of the cylinders - was a sticking point as I see everything from Aluminum 63's to HP 120's), with a flat bar crossmember to mount the roll control racks to. A lower crossmember to prevent the tanks from creeping under the tube. Rubber bungies to hold things more securely (if needed.) Cheap enough to build, but I never found time to get the boat in to my welder buddy to get it made.