Rowly, I have very similar plans for a cage (which did not come to fruition last year due to lack of time). I plan to flood the tubing and use "noodles," flexible closed-cell plastic foam cylinders about 3" in diameter and about 6" long(swimming pool accessories), to float the cage. You could attach the noodles around the perimeter of the cage to the netting "skin" at whatever height you wanted, using the same cable ties you use to attach the skin to the frame. I think the noodles would also serve as your feed ring, if you want it to encompass the whole cage. You can pick up noodles (during pool season) around here for $1 to $2 at Walmart, etc.


"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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