Thumbs up on a nice design. Several years back I built some brackets for attaching trolling motors to Kayaks. One of the things I did was to machine some circular recesses in the starboard transom mounting plate to allow the trolling motor round circular clamps to recess slightly into the starboard to lock the trolling motor in place to keep it from falling off of the kayak. Couldn't tell from the video what your mount looked like but you are welcome to use any part of my design to help you along the way. I have quite a few videos on my youtube channel that show how all of that stuff works. I don't know if I have a photo of the transom plate show in any of the videos but would be glad to send you a picture if it would be helpful.🙂