camping around xmas

Hey guys, I've been talking with some mates who are keen on camping 27th-29th December. They are pretty set on Sandy Cape just north of Jurien. I've been there and reckon it's a great spot, however I've been led to believe that school holidays, public holidays, and especially around Xmas time is completely packed out.

So, can anybody comment on whether or not arriving on the 27th would be a waste of time? I have a feeling just about everything within 3 hours of Perth will be choccas! Or does anybody have any other ideas? Would help if there's a dunny but we may not have a choice.
Cheers