Upper Right Photo: This plug is the injection port plug where the center hatch is cut out. This was from my kayak's center hatch but you could get the scraps from where a center hatch was installed at your Cobra Dealer for the asking. I drilled a 3/4 " hole in the kayak for the plug. I then drilled a 3/8" hole in the plug and then sliced the plug from the side to the center hole so I could fit the wires through the plug. I then sealed both the plug and the wires with "Plumbers Goop"
Lower Left Photo: Battery box, in it I use a 12 volt battery from a "Uninterruptable Power Supply" UPS for a computer. I recycled the battery from a overloaded UPS. I kept the UPS case and innards to use as a battery charger. Works great
Lower Right Photo: Transducer was glued down with "Plumbers Goop". The kayak surface was roughed up with 80 grit sandpaper. This is inside the center hatch under the seat area.  ~Ed~

Photo's courtesy of Ed Whited.