I have an older Outback. I also have a
TerraTrike Rover recumbent trike. After the first practice run with the Outback I realized my butt wasn't compatible with the seat. I made a simple mounting bracket for the Rover seat with a piece of aluminum, four seat plugs, and a pair of L-brackets. I had to mount two more L-brackets in the rear deck for the back support which limits accessories there. The seat sits higher, and it rocks a bit, but is stable enough for my river camping trips (I don't fish) even with a large amount of gear piled on the rear. The bracket has some design problems, mostly with the plug handles being too close to the brackets which makes them difficult to tighten. I'm making a better version soon.
I like imerc11's
Jackson seat idea however I dislike backrest support straps. My past experience with a stadium seat in a canoe was bad due to the buckles slipping, even with the loose ends tied. The Rover seat is a full frame but unfortunately is not available separately from the trike.