You could always do what we did: rent a 4wd car or camper from Britz and drive across the north of Queensland through Hell's Gate Roadhouse to Darwin. We took about 2 weeks for this trip and included several national parks (best known of which was Kakadu). This trip is only doable during winter in Oz, otherwise too many of the roads are underwater.

Britz does one way rentals which are more fully stocked with camping equipment than their website would lead you to believe. Be sure to rent a satellite transponder in case of emergency or, better yet, an Iridium phone.

This trip is not inexpensive, but it sure is unusual. It is best if you have experience driving off-pavement before undertaking this trip. However, the road conditions posted on the auto club websites turned out to be overly conservative, the roads were better than expected. There are other precautions, such as: Do NOT get out of your vehicle when in, or within, 5 meters of a river or lake. (You will be in some rivers since the roads cross them and not everywhere has a bridge.)

This is not your everday tourist trip. The sign at Hell's Gate Roadhouse reads, "Next fuel, 320 km."