So your Coleman instant up - do you think has good ventilation??
Hard to say, I don't have anything to compare it to. It doesn't have those little vents down low at sleeping height, but it does have big windows. Darwin in summer has big rain. Not a good combination!

We did some pretty rough camping, and never had a problem with the floor.

To get from A-B last time, Melb to Perth, we went via Dubbo, Sydney, Townsville, Alice Springs, Uluru, Darwin, Broome, Exmouth, etc. Highly recommended!

The west coast is amazing. Sparse, yes, places are much further apart than they look on the map. Rugged and beautiful.