A fisherman that sold me a GPS recommended the RAM system of mounting it and other devices and that was some of the best advice I've ever had. 

 

Using variants of them, I have two GoPro cameras and a GPS mounted in my boat, two dash cams in my cars, and a cam and RADAR detector on my motorcycle. Gads these mounts are terrific! 

 

From suction mounts that really work, to articulated extension arms (in plastic or aluminum), flat surface screw down bases, and ball sockets to swivel adjust to any conceivable angle, if RAM doesn't make one for your needs, I doubt you'll find one anywhere else.

 

If you haven't looked into RAM mounts, do so. The flexibility of this system is nothing short of staggering. 

Oh, I "thought" I attached a pics of them. On the boat I have one aiming at the front fishermen, and the other on the rear fisherman. I also have one on my hat. The boat I rigged up with a dual 18650 "battery bank" that will keep my two gopro cams going for over 8 hours. 

 

The car GPS is invaluable for finding fishing spots near the road I can hand launch my jon boat.

 

RAM mounts are ideally suited for lighter weight sonar units 7" or under. T-H Marine is the gold standard for heavier 9" and larger units.

Tom