Lightning Ridge to Broken Hill

David, I think you would be more likely to find some nice camping spots down the Darling River road than out through Wanaaring.
Come down through Bourke to Wilcannia.

With a bit of luck it won't be too hot, it usually starts to get hot in January.

Dave

Dave is right there is lots of good camping along the Darling.

But, the run west to Wanaaring and down through White Cliffs does have some merit.

Reola station is worth a visit, check out the "Big Shed". I would imagine that there will still be a bit of water in the Warrego and Paroo and that means wild flowers aplenty.

The other advantage with that route is that you can drive during the day with the A/C on and probably make White Cliffs for an overnighter in the underground motel, which would be cool. Literally

You could probably manage Lightning Ridge to White Cliffs in a day. Have a good look around White Cliffs before heading to Broken Hill, about 3.5 hours drive. Have a couple of days in the Hill and then head down to Mt Gambier. I would go down towards Mildura and then turn off towards Renmark just south of Coomba Roadhouse. I think it is Pinecamp Rd. It takes you down around the back of Lake Chowilla. Surprisingly it is not much slower than staying on the black top but it is way more interesting.

As for the heat, people live there all year round. They work, they play, all the usual stuff. Be sensible carry plenty of water, keep an eye on the temp gauge and take it easy. You should have no problems.

Duncs