I have an Outback and a HB 597ci HD DI. So, while not exactly your situation it is similar. I shoot through the hull just in front of my Mirage drive and behind the sail post. I use a well made out of Duct Seal and splash a little water in it each time. I put my battery in a dry bag and have it sitting on the floor of the kayak in front of the sail post. I do have two pool noodles in my yak that keep the bag in place side to side and the sail post keeps it from sliding back.
I just run the cables out the front hatch and then close it. I bungy the finder (which is mounted on a board) down on the front hatch. This setup has served me well.
I hope this helps a bit. Here is a pic:
You can see the black wires that run under the board to the back of the FF. This works well due to the fact that the hatch is a bit concave. Thus, in my setup I have nothing permanently mounted and no holes drilled.