I probably won't be going for a few years yet, but if you could inform me of where I might be able to get some of the paperwork from for future reference that would be great.
Primarily you need two things for the Australian side of travelling with a firearm:
To export the rifle, you need a restricted goods permit (
http://www.customs.gov.au/webdata/resources/files/formDEC07.pdf) which is lodged through customs. You also need to be registered as an exporter on the customs database. Customs will only issue this permit within 30 days of your departure date, although it only takes a week or so to get this issued.
To reimport the firearm (ie bring it back with you), you need a B709A form issued by your state police. Just search the web to find the version relevant for your state. I get mine from the Vic police, and it usually takes about a week for it to be issued. I had to wait a couple of weeks once, but generally the Vic Police are fast. I recently heard of someone waiting over 9 weeks for this permit to be issued by the NSW police, so it is very much dependent on the given state.
Also, bear in mind that IATA rules limit you to 5kg of loaded ammo, and airlines will ask you how much you have when you check in. Airline rules will vary, so talk to the airline well before you travel to make sure you can comply with their requirements. And make sure you know the rules, as not all airline people do - I have had a few arguments with airline staff in my travels.
When you exit the country, you must get your AGP stamped by customs at your point of departure (ie the last Australian airport you transit through. This can be painful, but if you do not have this stamp, you WILL have trouble when you reenter the country on your return trip. When you reenter the country, get your bags, then go the "anything to declare" aisle and customs will want to see the AGP and the B709A forms before they let you take your rifle case.
It all sounds like a pain, but it is not as bad as it sounds. But it does change, so if you are still a few years from travelling, this may no linger be valid by the time you need the information.