RACV gets 10% off for long term parking at Tullamarine (Melbourne) Airport.
1 - Click on the Tullamarine Airport button
2 - Enter when you want to park and pick up
3 - Select Melbourne Airport Long Term parking (should be in the list somewhere)
4 - Membership number and surname
5 - Get taken to Melbourne Airport parking website for final pricing and discounts
Other types of parking get discounts too
Also lists discounts on airport transfers in some Queensland and NSW locations, on that RACV page.
Cheers