Best thing would have been to confirm Auckland at the end of the last cup and built on the momentum plus giving confidence to set a campaign around.
Not a good way to get anyone to commit when not even the host club knows what’s going to happen
I'd use urethane skateboard bushings. A lot of early mountainbike suspension systems used urethane bushings as the "spring". Stable, takes huge load, available in a wide range of compression strengths (duro), easily replaced and tuned (stack different duro bushings in different lengths to tune).
You will still need a topping lift. Even the best systems only support the boom temporarily. Without a topping lift your main sheet won't have anything to brace the boom against and it will swing all over the place
We used to use squash balls under concrete pavers to support turntables in nightclubs/dance parties etc. We replaced them every month or so. They rapidly lose the air within and quickly become a mush of rubber when under constant pressure.