danbob;
In lookiing at your set up I have an idea for the fish finder mount. I have an ODC 816 and the frame for the seat is almost identical as well as the seat. I raised the seat by modifying a bass boat swivel seat mount. I have filled in the open space with white plastic peg board and carry the battery on one side. My built in saddle bags are not as big as yours so I could mount the fish finder on the other side, under the seat and could open the screen out to the float and be able to look down to see it. I wish I could post pictures!!
I've also built a rod holder out of pvc pipe that protects the rod while keeping it well at hand.
I'm going to see if you have your email in your profile.