Not using phone. Does not work in area. Looking for stand alone thing. is that right? On dash,screen,showing where we are/have been.
A phone works fine. You just need an app that uses offline maps. There are many. I may have been the one who turned
@campfire onto BackCountryNavigator and it may still be the biggest value in terms of free maps and imagery. Pretty much any of these apps can store and read tracks. They vary from sucktastic to awesome. A dedicated GPS unit (Garmin, DeLorme, TomTom, Magellen) may be more stable (i.e. less likely to crash while recording your tracks) and easier to justify leaving in the vehicle full-time, but some of them have expensive or non-existent maps off your trails. Now you don't need ANY map to store and read tracks, but it makes the device harder to use. You can leave any old GPS unit mounted in the vehicle to record where you've been and show you pre-made tracks, as long as you can move data on/off via an SD card or Wifi. That's really all you need to follow yourself back out the way you came, or follow the same route somebody else took and emailed to you. A tablet/smartphone is more convenient in that you can display, store and manage data on that device.
For exploring new areas I'm a huge fan of having pre-downloaded satellite imagery hybrid with the USGS trail maps. Sometimes you can see points of interest or open trails on the imagery that isn't on the maps. In heavily wooded areas, imagery alone isn't enough. There are also areas where any map data is over a decade old and most of those trails are gone or closed. Sometimes the only way to have a map is drive through yourself and store tracks. You can try 20 dead-ends, find one good way through, then go back later and edit your track to only have the valid route. I also like putting a "push-pin" (GPS marker) on things of interest, like gates, downed bridges, waterfalls, etc. to remind yourself of what's down those dead ends.
For these more advanced tasks like editing tracks, splicing them together, making tracks by hand from maps, etc. you'll end up on a PC, though.