Subject: Caravan Park - Sydney

During December we are planning to travel with our caravan from Perth to Melbourne. Then take the boat to Tasmania for three weeks. After returning to Australia proper we intend to drive to Sydney. As we have never been to Sydney I am not sure about driving right into the centre of town. My question is this: does anyone know a good caravan park just outside Sydney from which we can take public transport into the city with, say, a three quarter hour maximum journey time? Thanks in advance Gerrit - Perth