I'll toss out another software solution, Gaia GPS. They have apps for both Android and iOS, you can also use their website which is extremely handy for planning out routes. Has offline maps that you can download to the device, you specify the area and the detail. They also have a number of layers that are really handy; Gaia Topo, USFS 2016 (CalTopo), USFS, Satalite, etc.
But I agree on using a tablet or a phone as a GPS device. Puts more functionality into the package with all of the other things you can load onto them like campground maps, trail maps, etc.
For mounts, I have my radio and my phone that I use for GPS riding in a ProClip system that attaches to the dash. I'm really happy with that setup.