I prefer an original gimbal type mount. (i've made my own, but you can buy replacements). They don't typically come loose. You will need another set of power wires and nema cables if you are linking the units. And another transducer. Which you can place on the drivers side of the transom since you are only using it for trolling. Unless you switch the console unit to 83mhz while both are running, the 2 units would cross talk.
I've had units pop out of Johnny ray mounts. Rams can come loose.
Easier to just turn around and look at your 12" screen.