We used Wiki camps initially, it is handy as reference, but in general started looking for places to stay which were not indicated on Wikicamps. As these places were a lot cleaner. There are quite a few disused gravel pits and after a while you to start seeing the entrances. One really nice free camping for a few days is the back half of Albert Tognolini lookout east of Karijini NP. Start looking from about 3pm. In general if getting within 50 km of towns leave it to the next day so you have time to stock up and get camping the other side before it gets dark.
Cleaverville east of Karratha is nice by the water, you pay at the east end it is cheap. There is a small proper caravan park in Dampier if you want to look at Burrup Peninsula. Around Broome is hopeless. Best to drive up to Wille Creek or James Price Point, around Derby is difficult as well so get your timing right.
If you still wanted to do the west end or GRR, Bells Gorge camping ground in not expensive and there is free camping at the junction heading south to Windjana Gorge. South of Tunnel Creek there is a large gravel pit and a bit further an area around boab trees.
Roughly half way between FC and HC there is free camping. Sawpit Gorge out the back of HC is nice. The road is similar to the west end of GRR.
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My two bobs worth,
I personally wouldn't miss doing the GRR, people over exaggerate on some of these roads.
We have seen all types of caravans and camper trailers on all of these roads without any problems.
You just have to drive to the conditions, slow down and as I say smell the .
If you don't do that what are you not going to do any dirt roads in your whole trip and miss
most of what the excursion is about.
But then if that is what you want it's totally up to you.
I have been along the bitumen from Perth to Darwin
There are plenty of free camps, some with toilets, some without
As others have already said, Wikicamps will show the free camps
Camps Australia Wide book 9, (new editions comes out about February 2019), is also very handy
I know nothing about fishing, but I did not see the Ocean, after leaving Derby and entering Wyndham
Have a good road trip, but plan for the weather, it gets hot across the top, in the summer time
