I installed my Garmin GPS and Fishfinder using a RAM Mount, I saved from my last boat. This kind of a mount provides a lot of versatility, you can position it any way you like.
I like to point it downward so I can see the GPS from the berth. Im always a little paranoid while on the hook trying to sleep, concerned I might be dragging anchor. I can just look up from the berth and see the trace line giving me piece of mind Im still in the same spot.