I have a 2013 PA-14, so I believe the under seat storage is a bit different from your 2011 PA.....However, I too did not to need to "fish" for my tackle box under the seat or lose it while on the road.
The 2013 PA has a nice adjustable strap and only one tackle box....I bought a second tackle box and then drilled a small hole in the back hinge-mechanical rib, where I attached a small nylon line that is 2.5' long....terminated the other end to a eyelet post under the seat.
On the road, when the strap was cinched up, the tackle boxes would still move forward out of the strap......so I made a simple retainer/stop using 1" OD PVC pipe....the pipe drops down 6" into the scupper holes and will not jump out as the seat is secured in the down position.
I used old wine corks to stuff the PVC pipes in case I dropped the retainer into the water.
If I had forgotten to remove the retainer while fishing, the seat front only need to be lifted up an 1 inch or so and it comes right out of the scupper holes.....