Buzzy,
When they don't have the people they can't man. The solution is to hand it to ASA and move the RAAF controllers to other bases. It would assist the other RAAF bases that are not fully manned.
I'm yet to hear a specific reason why RAAF members have to man at YWLM. Sure you need to keep a certain number of controllers current for deployment purposes, but when you don't have those numbers what exactly is the reason for RAAF members to man tower?