Here is what I did for the two cushions on my boat that don't have hinges and just pop on & off - for when I am transporting. You can see the U bracket I installed on the starboard I used for my Norco Charger. The second is bolted to the aluminum frame. Then, as I can be absent-minded, I put in a leash as a redundant backup - though if it flies, I assume that little Uring will rip right out of the bottom of the seat...
Nice job and good suggestion. It would be a pain to replace plus the safety aspect of having that cushion fly out at a car following you down the highway.
