The WEA have now been able to make the parking out the back available for us on Sundays. We will still have to pay $4 (must be coin for the machine) to get in.
We have a key to unlock the big gate. Once this is done (by 9.45) you can enter as per usual and pay your $4 to open the boom gate. When you leave (which will need to be soon after the service), once the exit boom gate goes up, just drive slowly through until the big black gates start to open (they will open out toward the footpath and away from your car) and then you can drive out.
Thanks to the WEA for this service!