Hi Rob,
Print out page 2 of this form and bring it along with $50 on the day, They'll submit the form and payment for you. I'd say to apply directly to AASA, there's still time to do it before the event and recieve your membership card in time, but its better safe than sorry in case AASA processing is delayed for any reason.
http://australianaut...PPLICATION1.pdf
As for the fire extinguisher, it needs to be securely mounted within the car within reach of the driver.
It's been discussed many times before, but to summarise...
Get a 900gram+ Fire Extinguisher from Autobarn which has a metal for mounting. (~$40)
Go to bunnings/your shed and get some aluminium strap (1mm thick x 30mm wide x 50cm long) and.make a car bracket which runs between the passenger seat front bolts. Bolt (with decently strong bolts / washers) the extinguisher bracket to the car bracket.
If you position it right, it won't interfere with the seat movement along the rails, and it'll be easily accessible if needed.
Whenever anyone gets in your car for the first time they'll say "Why do you have a fire extinguisher?!" and you can casually reply "Because Racecar."
In the past some people would tek screw it to the floor or the trans tunnel or console lid. In an accident they'd rip out straight away. So this WILL NOT pass scrutineering on the day.