Hi Al,
I am not sure if you would be allowed to camp on site at such short notice. They actually run a business there during the day, its called "The Paintball Place". Its at Kulnurra just off George Downs Drive. You could camp about 20 to 30 mins drive away in the Yengco National Park, there are 2 camping grounds that I know of (haven't used them) at Mogo Creek and Finchley Trigg. Check the internet or with Parks and Wildlife for more information and maps. You are also less than an hours drive to seaside resorts like "The Entrance", "Terrigal" and "Norah Head" from there.
You are more than welcome to attend, you just need to find a camp site. Someone else may be better able to help you out with the camping aspect. Last time I went camping the park had a big "Novotel" sign out the front
CS-John B