I used an old stadium seat that the previous owners of our house left behind (that's why they say Alvord Bulldogs on them). I added a piece of aluminum stock that I had laying around my garage to attach the rear feet but any bar stock should work.

I made the feet using stainless bolts and rubber boat trailer rollers that I cut into halves. I had these already on hand so that's why the rear feet and the front feet are different. I like the front ones best


and they're actually the end caps from this type roller
https://images.app.goo.gl/prVx9Sj9BjF5uGXD7
I think someone can figure out my process from these pics.











I have seen some different ways that others have used to add seats like these but most used a rail of some sort bolted across the width of the kayak on top of the side beam. I didn't want to drill into mine (plus theres really not a flat area there to bolt to) and I wanted the seat to sit as low as possible to keep the center of gravity lower. I used the cut rollers because they are a wide base which distributes the weight better, and rubber so it's easier on the plastic boat. If anyone has any questions, just ask.
Oh, I also added these rubber grommets to the sides to keep the seat centered and keep the metal sides from damaging the boat



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