I have a Handheld Garmin GPM Map 76CS, we fab'd a handle to mount on the roof using the existing bolts on the windshield hinge. I have it wired into the 12v system when the engine is running and then if the engine is turned off it reverts to it's internal battery.
Here’s my TRX 7. it came with the suction cup ram mount and I put one of those adhesive suction cup pads the cover of the cubby. Works great and stays in place. Easy to read too. I run a power cable for long trips as the battery only lasts about 3 hours.
I use a Galaxy Tab A 8.0 (GPS and WiFi only) with Gaia GPS and OnX Offroad apps and a combination of Ram tablet holder, Tackform cup holder mount and arm in our Lone Star. The cup holder mount lets me move the tablet over to the other side for the navigator (wife) to look for new trails to explore.
Costco had the Tab A on sale for about $85 a couple of months ago so I bought 3.
Good luck and enjoy.