I installed a Canon mini-lake troll....manual hand crank down rigger on the left side, just forward of the molded in hull rod holder on my Outback.
You need to make sure that when drilling or cutting into the hull, you do not run into cables on the inside....that could be a critical error!
I also found out the first time I used the down rigger , the kayak wanted to track to port due to the new/extra under water drag....I use a 2.5 # lead weight to fish at 30 to 80 feet depth.....solution is to install the sailing rudder......a cheap $22 investment that does the trick and tracks like a dream.
I picked the Canon as it has a line counter on the end of the arm/pulley to easily see how much cable is deployed.
An electric unit was out of the question for me.....extra battery required and the possibility of dunking the motor at some point.....not worth it....so I now have a larger left arm!