I can't attempt to beat the record for the longest trip, but maybe of interest here.
In 1973 and 1974 I made two crossings of the Nullabor about 2000 miles from Melbourne, Victoria to Perth, Western Australia in my 230sl.
In those days there was about 800 miles of gravel road between iron Knob in South Australia to about 100 miles East of Norsman, W.A.
The road conditions varied considerably as the photos show, in dry conditions there were "bulldust" holes two foot deep which turned to slippery water holes when it rained.
One photo shows us parked beside an emergency water catchment and tanks.
I actually did this trip 3 times between Melbourne and Perth, the first however I put the car on the Indian-Pacific train as i didn't want to put the little 230 through the trauma.
One crossing (the last in the 230) I hit a kangaroo, or rather it hit me in the drivers door at Baladonia, so I had to drive about another 400 miles with the door held shut with some rope.
I sold the car in Perth, I have previously put a request on this forum to see of anyone knows who has it these days.