Moonie Beach Caravan Park (has big treed area for tents, camper trailers), or Red Rock (Just north of Coffs Harbour)
Awesome beaches around that area.
It's about 350 km from Brisbane, 5 hours? so could be your last stop before getting back to Brisbane. But i'm sure there's better spots, just not sure of any.
my dodgy blog www.shackers.net