Plenty of caravan parks in Kununurra.
Also a caravan park at Lake Argyle - which is worth a visit.
National Park campgrounds are cheap - at Keep River NP (about 18kms of gravel road to get to the first campground - usually ok for 2wd. Very scenic). Caravan parks at Timber Creek and Victoria River Roadhouse. Small NP campground just off the hghway, a bit east of Victoria River.

There are several free camp areas out of Broome - Ellendale, Mary Pool come to mind. Caravan Park at Fitzroy Crossing, also one in Halls Creek. Free camp area where Ord River crosses highway, north of Halls Creek. Caravan park by the turn off to the Bungles. Also, I think, at Turkey Creek RH.

I agree with Wendy. You shouldn't have any problems finding a place to stay. In 2015 when we were up that way it was prime Grey Nomad travel time and school holidays and we never booked anywhere to stay before hand. Sometimes we free camped and sometimes stayed at caravan parks. There was always other campers in the free camps. Never felt unsafe anywhere we stayed. At Fitzroy Crossing we stayed at the CP in town next to IGA. We got a discount at IGA for staying there. We had no problems. Presuming you are going out to the Gorge may I suggest you do both tours. We went on the national parks tour in the morning and the indigenous tour in the afternoon. The gentleman who took the afternoon tour was very informative, we saw lots of crocodiles (only one on the morning tour) and there was only six of us and the afternoon reflections were superb. The tourist information centre in town was very helpful. We had wanted to do the coach tour to the Bungle Bungles from Halls Creek but this was booked out a few days in advance so we missed that but we bit the bullet, budget wise, and did a helicopter ride from Warnum (Turkey Creek). Loved it. Kunanurra show is on the 13th 14th July. We were there show weekend but found a CP site in the first park we tried. Between Kunanurra and Katherine we free camped. Stayed at the CP at Katherine Gorge. Hope this is some help even though it's been three 3 years since we've been there. Cheers.

This section is no more problematic than any other outback road. It is no worse than the Stuart Highway, which is fine, nor the roads across into Queensland from Threeways. Normal security precautions, such as locking the van and car, or motorhome, at night, or when you leave it for touring, and all should be well.

There are decent caravan parks at Roebourne Plains outside Broome, Derby, Fitzroy Crossing, the entry to the Bungle Bungles, Halls Creek, Kununurra, Lake Argyle, Victoria River, Timber Creek and then Katherine..

There are also free camps at Marys Pool, entry to the Bungle Bungles, and the corner of the Wyndham Road and Kununurra Road. There are many others, but I know these 3 are well used and popular.

I am afraid that many trips, like the thread about the Nullarbor, see what are normal roads and drives, albeit over long distance, being given some mystique as being a test of endurance. They are not, as long as you take some simple and normal preparations to ensure the vehicle is ready.

We did that stretch a couple of years ago & had no issues with caravan parks (noted some nice free camps too, but you had to stop early).

Wendy mentioned the Lake Argyll CP - it has a magnificent "no horizon" pool where you just lie in the COLD (to me) water & gaze over the Ord River & associated scenery. Caravan parks in the larger towns in their tourist time (now onwards) are expensive.

We enjoyed two flights in the Kimberly - the first was a helicopter ride over the Bungle-Bungles (out of Timber Ck) & the light aircraft flight (North West Bush Pilots) from Derby over the Horizontal Falls & the Buccaneer Archipelago. Sure it would have been nice to do the sea-plane & boat trip through the falls but we had an enjoyable time anyway.
Pat thought it would be nice to drive into the Bungles - never again!! The flight was much better, less stress, more enjoyable & relaxing!! (Where do you go on a narrow, rocky & rough road when over the next crest comes a huge AAPT 4WD bus, driving as if they owned the road?)

Geicke Gorge - just outside Fitzroy Crossing is a tourism feature, and well worth seeing. We did it a number of years ago, on a boat trip run by the National parks. Seems like there is now more than one tour option there. It is a long gorge on the Fitzroy River - multi coloured layered rock, die to wet season water levels, and lots of freshie crcodiles.
At Fitzroy Crossing, we prefer the caravan park out on the highway - just on western side of the bridge over the river - hotel/motel at front, caravan park in behind that, very pleasant.

Zebra Rock Mine and camp on the NT side of Lake Argyle is also good. A quiet safe safe camp where they do tours our on the lake as well.

We had a break in At Halls Crossing while parked opposite IGA. In daylight . Lucky I was inside .. Had NO issues free camping around Gov side roads to repeater towers etc . Always parked face out . So any problems we could just leave . Plus see anyone coming our way . Often off road enough that cannot be seen by traffic .