For anyone travelling to this meeting and wishing to avoid the traffic delay, there is a Country train which is due to leave Campbelltown Station at 12.04pm then Macathur station at 12.07 (Both have parking available) which arrives at Menangle Station opposite the main gate entry at 12.12pm.
Ron, from Rydges which is mid stations, travelling time to either is 3 to 4 minutes, allow 10 to include parking.
This could be an option.