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Not a good option for a sea kayak..
The seat will NOT stick into a fiberglass kayak no matter what you use. Glue, velcro, nothing works. The minute you brace with your feet it dislodges. Also there is no thigh support so you have to figure that out and if you use any screws the seat is so flexible the screws will tear.
Last comment is the seat is too high for a sea kayak. So unless you are a craftsman who can shave off a lot of the bottom without ruining the seat, the boat will wiggle as your center of gravity will be too high.