How does this work?
As you postulated, just set up an account with the forwarder (free) and have your purchases addressed to yourself at the forwarder's US address. From memory they are set up so you pay no US domestic sales tax and also offer a purchase service for retailers that insist on payment via a US credit card and/or billing address.
Then just let them know the details of your purchase(s) and they will consolidate and re-pack your goods for shipping to Australia. The other good thing about MyUS compared to most other freight forwarders is their shipping charges are based on actual weight rather than volumetric weight, which is good for large/bulky items that don't actually weigh that much (e.g. spoilers, decal/stripe kits, etc.)
Only downsides I'm aware of are their per kg shipping rates are higher than some others (in spite of what they tell you) and I'm pretty sure you will be paying GST on everything you buy where that's not always the case when you ship direct from some of the smaller US retailers.