Marina's on the coast are allowed to allocate up to 6% of their boat pens for live-a-boards, but it still takes an application and permit
(and additional monthly fees). If you are a visitor from out of state their are some special rules that make it easier for a season. A live-a-board here is someone who sleeps on their boat more than six nights per month. There was someone on the forum a while back who knew of all convenient anchoring
spots - dig a bit here and you might be able to contact him for the local knowledge. It's extremely hard to get a pen closer to Perth than Mandurah or Mindarie anyway. Port Geographe could probably accommodate you.