Tried to find some pics of the barley cage before it became structure but elude me. The cage was 14 ft long 4 ft wide and 4 ft tall. I had the legs at 4 ft with 6 ft in the center unsupported but had a center frame as yours.Im guessing the inside lower part of the T's on the bottom broke out. It worked fine with 150-200 lb of barley in it as the material floated as did the cage.It had 4 inch pvc on the top rail that kept it stable and afloat. I monitored hydrogen peroxide levels and could not get them above .5 ppm (3 needed for good algae control) so structure it became. This cage had an aeration tube running down the center and was modeled after a unit built in the UK after conversations with a professor named Johnathan Newman who has done more work with barley than anyone I could find.I think any kind of center support would work great on yours and as you state "prewater" is doable later is a pain.