Hey Spiceweazel
I think there is a thread on ttmaps on the forum. I have an older tom tom and use it on the tracks in conjuction with my paper maps. Below is the search results for you to do some more research
4x4 Earth Australia for 4WD Tracks
It doesn't have the track names on their maps but has most of the tracks. Being a destination based system can't program destination unless using the coordinates. I found that this sytem isn't too bad got within 15 metres of the entrance to a camp ground which isn't too bad.
BUT QUITE SIMPLY DON'T TRUST THESE THINGS IN ISOLATION IN THE BUSH