I did Mungo by car camping in winter a few years ago. Accessibility was not a problem. Only the achingly cold and frosty mornings were a challenge. I thought a week at Mungo was too long so I went down the road, turned right, and spent the other half of the week at Wilpena Pound in South Australia; more cold and frosty landscapes but truly dramatic as well! And do the Cazneaux Tree if you go down that way.