I have a personal opinion that cats should not be taken into the bush, Notwithstanding, I am aware that there are some that adore their feline friends and must have them with themselves.
As long as your Mates, are certified as de-sexed, can accept being harnessed at all times whilst out of your vehicle or caged, you shouldn't have too many obstacles taking them along.
Many caravan parks will not allow your feline pets even though they advertise as pet friendly - so you will need to ring ahead and speak to the proprietor/s (not just a receptionist). National Parks will be definitely off your visit list unless you just walk in to see a particular attraction. I am uncertain of the State Border Regulations concerning cats you will need to check all differing State Regulators. There are also the problems associated with Feline Calicivirus you will need to be aware of en.wikipedia.org/wiki/Feline_calicivirus also take care in remote areas that your animals don't pick up Baits laid for wild dogs, the areas that baits are laid are Regulated to be adequately signposted but there are many areas that don't have signage.
Enjoy your travels and be aware that there are many out there that will berate you for having Cats on board.

We saw an incident with a cat in a caravan park.
We were out in western Qld last year in a park and their was an elderly couple there that had a cat. The park rules seemed to be a bit slack and there was some dogs that seemed to be free to roam around.
Unfortunately one of the dogs took a disliking to the cat and decided to chase the cat. The cat ran away out of the park and the owner of the dog called it back and tied it up.
Sadly for the elderly couple the cat did not come back, we were there for a day or two after that incident and the couple were distraught that the cat was gone. The dog owner gave an impression that he thought it was funny that his dog chased the cat away.
It was suggested to the couple to wait at the park until the dog and the owners left and then the cat might come back. We dont know what happened in the end because we moved on.
What we have noticed in our travels is that there are many people with animals who arent responsible enough to control them.
Just because a park has rules doesnt mean that these rules will be obeyed. If you take your cats on your trip just be aware of other owners and their animals may not be following the on the lead or tied up rule.

Hello ronjons

We took our cat (from 13 to 16 years old) with us on a few trips, and had no problems

But....

Always had a harness on, (two leads length tied to the table leg), she had enough slack to reach the driver and/or passenger seat, and her dirt tray at the rear

We only took her outside (with the harness still on), while carrying her

Never went to many caravan parks, and never asked if animals were allowed

We would just tell her to keep a low profile, and stay quiet

She always gave the same answer Me! How?

I have been traveling with 2 cats for over 6 months now. Both are fully harnessed at all times. Secured to the seat belts in the car. Both will walk on the leads but the female is not keen on it. The male is slowly getting used to the idea & likes to get out and explore sometimes. I am always wary of loose dogs. Unfortunately I have seen loose dogs in most parks. You just have to keep an eye out for them. The travelling has not really been an issue although they can get a little bored & want attention after a while.
I also built a small cage which attaches to the caravan boot & made a doorway from the van ino the boot so that they can get out of the val without being tied up. The Male cat loves to lay in this & watch the world go by.
So far I have been refused access to 1 park, In southern Victoria. The rest have been fine once I have told them that the cats are on a leash or fastened in the van all the time.
I have noticed a surprising amount of cats traveling since I have been on the road.
Oh and as for the story of the runaway. Both cats have escaped the van on more than one occasion ( Cats are good at that ) & both have been chased by dogs. But both also know that the Caravan is home and do not leave the immediate area around the van except if chased . ( both by my daughters dogs ) They normally wait until the coast is clear & return to the safety of the van.

-- Edited by Stuart-Jan on Saturday 26th of May 2018 04:09:15 PM

Thanks for all your input. Well so far so good with 1 cat.Tinker is her name, she is a well behaved cat, hates the harness and doesn't like people or noise and there is a lot of it in caravan parks.

Thanks for your replies. Wow 17 year old cat is a good age. If you see this again please put up a pic!. Ive left one here of my Tinker and Chad (he is not with us yet) Chaf has cancer so we are waiting to see what we do once the business sells. 
Cheers
Ronnie

Actually they are the good friends for us, if I were you, I'll take them together. But just keep them in the cape on the RVs. Maybe a bit noisy.