I mount mine right on top of the Sonar Shield, with a couple of screws to wingnuts (for fast on and off).
I run my wires into the hull thru a Cable Clam just underneath the cover. Drill holes, in the rubber piece, about the size of the cables you are running thru them. Slice from the edge of the rubber to each hole to get your cable in place. The action of the Cable Clam will tighten everything up to seal. My transducer cable goes in and then back out to keep most of the wiring inside, out of the way. It is all zip tied above my OK battery bag.
For next level, you can install one of the giant transducers on the bottom too.
