The free camp at cooktown is very dissapointing, you must have not only a black water tank but also a grey water tank and your van will be inspected by a very zealous ranger. If you meet the requirements you can stay for 2 nights. It is also on a dirt road that carries a lot of traffic making a lot of dust and noise, making the stay very unpleasant. They also have camping 10k out of town at the airport grass but no other facilities including no water.