An alternative to a snorkel would be two carry a spare air filter. At the end of a (dusty driving) day swap out the filter element and place the filter dirty side down in a plastic bag in the trailer. The next days corrugated road driving will shake dust out of the filter and again swap it over at the end of the day, and so on.
The GRR is in pretty good condition these days and carries a lot of traffic, headlight covers and windscreen/glass insurance cover would be a very good idea. Duct taping corrugated cardboard or core flute (the plastic corrugated 'cardboard' that real estate signs are made of) over the rear window(s) could save a heap of grief and expense. Broken rear windows are a very common problem when towing with a wagon type vehicle on stony outback roads.
The Pentacost River crossing near Home Valley Station is has excellent approach and departure access with a good gravel/smooth stone and flat bottom. Like all crossings on the GRR taking it SLOWLY will see you OK.
It can be quite corrugated going up to Drysdale Station and VERY corrugated between Drysdale and the Mitchell Falls turnoff but well and truly worth the effort. Again driving slowly will see you through.
The 18'' offroad tyre/rim combo would be a good idea.
My two bobs worth.
Deano :)

