In reply to Aigen:
I'm not sure about any SatNavs that will offer good GPS navigation for driving and exploring offroad, hence you might be better off with an Android phone/tablet with a chunk of memory/SD card slot rather than a specific Sat Nav.
Here Maps (think its called Here WEGo or something now) offers the ability to pre-download maps for areas you need on a per country or per area basis, rather than the Google Maps approach which is quite tedious to download large areas. Mapping is pretty solid, although I don't know how well it'll fare with 4x4 tracks. Its gotten me across South Africa multiple times and generally seems to know all the paths in game reserves etc.
Combining this with Viewranger or GPX Viewer or Maps.Me (I think this offers offline mapping, but only supports KML files rather than GPX) for following premade trails for non mapped roads.
Post edited at 11:20