GPS Unit for use in Car

AS an alternative to a Mac / iPad software solution (see other post in this forum), what are the best GPS units to buy for use in the Outback. I'll be off road in SA, NT and QLD for about 2 months.
Part two: I live in the US. Can I buy Aus maps for the areas I need (in the detail to get off road and onto tracks) and load them onto a US purchased unit, so that I can plan before I leave?
Cheers
Graham
Part two: I live in the US. Can I buy Aus maps for the areas I need (in the detail to get off road and onto tracks) and load them onto a US purchased unit, so that I can plan before I leave?
Cheers
Graham