Clothes needed for WA-roadtrip

We are three norwegian students who're planning to do a surf/road-trip up and down the coast of WA from the end of november until early/mid april. At the moment we are planning on driving as far south as Esperance and as far north as Gnaraloo.

We intend to camp most of the time, living out of a tent and a car, but we are a bit unsure about what to pack clothingwise. What are the nighttime temperatures like during this period? Does the temperatures fall much in the more desertlike areas?

What kind of sleeping-bag would be recommended?

If anyone could help us with this, or if you have any other advice regarding our trip we would be very grateful.

thanks in advance

Adrian