I've been looking at similar options. Not sure if you have Hydraulic Steering or Hydraulic Assist or just mechanical, so that will make a difference.
One option I have looked at is an AutoPilot with a remote control like the TR-1. You wear the remote around your neck, set the boat on a course and have the ability to control the throttle, steer and resume course -- nice for fighting fish. Even has some pre-programmed trolling routes (e.g. zig zag down a line, or keep over a spot). Works in both forward and reverse gears so would be very handy for back-trolling.