The seat is visible upon station 5, center lower pic.
It's a simple rectangular piece of pvc skin, the alu tubes are slid into the two opposite hems I've sewn along smaller ends.
A high paddling position can be achieved by hanging the seat from the sheer stringers, or a low-CG position is obtained by sliding one chine stringer into one hem, turning the cloth over the opposite chine, and securing that spartan contraption by sliding the center keelson stringer into the remaining free hem.
The spacing between grommits varies: the larger at coaming-to-skin attachments, closer at deck skin lacing near the cockpit, where the pull is maximum, intermediate at aft deck lacing near the rear stem.