You need to use the address of a family member, or good friend, as a mailing address, letters and documents can be scanned and emailed to you.
Your address to Centerlink becomes "No fixed address".
Pay car rego's insurance etc online.

I use my brother's address. They open all my mail - not that there is much now with all the online bill paying available. Works really well, but I do recommend having a cheap scanner/printer so you can print, sign and scan to email any documents if necessary. No doubt there are places [Community Centres] where you could do that instead if you save to a USB stick. I also get them to redirect things like pension cards to a post office if I am interstate, as long as you remember that it can take a couple of weeks for mail to arrive sometimes.

Have been on the road for 4+ years. We use my daughters address for residential purposes and use a mailing service as a postal address. Sure the mailing service costs extra but it is very convenient. Sometimes we have to talk direct to an organisation re our postal address as their online address change does not accept our ID for the mail service.

register as itinerant if you want to avoid voting too