I'd find the spot you want to place it and do a custom fit basic board as a back up. Maybe cut out for any items under it to help lock it down.
There is the magma stuff that keeps it over the side that is a pure buy. I have one, pretty decent except you lose a rod holder.
What Rob posted above, except mine mounts in a rod holder and the gimbal base lets you angle it so it will drain over the side. The base folds up and it will fit in the center console.
If you planned on using the board just occasionally, you could shape something out of starboard or maybe epoxied plywood to go over the railing that guards the splashwell. It would have to be narrow enough to allow tilting the motor up. Maybe I saw that on this website. Or just remove the cushions in one of the rear seats and cut bait on that.