In my van, I use a Samsung Galaxy Tab 4 7.0 tablet, mounted on a Ram X-Mount and arm on the doghouse/center console.
The built-in GPS is more than sensitive enough. I have a dual-outlet USB charger to keep the tablet batteries mostly topped up.
I use the Backcountry Navigator App when away from the highway, and Navmii and MapFactor for on-highway navigation with preloaded maps. (Wi-Fi only tablet)
I also usually have my Nexus5 phone in a cradle, so if I need online maps like GoogleMaps or whatever, I can use that, which is also fine. The bigger screen is really most handy for looking at topos, etc. so off-road is when the tablet gets the most use.