I 'd be using
these for the bottom end as they hold all your poles at the right angle to drop on your cage. Use the twin ball/ socket pairs for the top. Too easy.
Heres a link showing a
minimal 16" project: its always good to see how people handle functional weight extremes.
Capral Aluminium in Sydney have 1" OD X 1.2mm wall , I'm not too familiar with Melbourne suppliers. You'd find that you'll need to machine the inserts for 1.6mm wall. You could also send Moonlite an off- cut as they'll machine for $1.50 each, though obtaining some 1.2mm would be the best outcome.