Coffs Harbour is a great place to stop. There are a few different spots to stop and I didn't have any issues with overnight parking (trying not to bring much attention to myself of course). Now only issue with these spots is the public bathroom gets locked up overnight so make sure you do your business before bed!
This parking lot is beside the WWII Coastal Observation Bunker.
Note: No bathrooms here.
Another spot I stayed at in Coffs Harbour was the parking by the Jetty Beach on Jordan Esplanade. There are bathrooms here (they get locked up overnight) but you can walk straight out onto the beach and there are lots and lots of trees to keep it cool during the hot days.