This time of year Coastal and Quiet don't really go together.
Victoria might be a small state but are you really considering the whole coastline as possible camping location ?
Lakes Entrance & Warrnambool would have to be two of the more crowded / touristy places in Vic during summer.
Can you narrow it down to East or West of Melbourne ?
Some national parks have long waiting lists for camping reservations.
When you have to wait a year to sleep next to a tree, something is wrong. ~George Carlin