Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4971039.
I had been using two pieces of PVC held together with zip-ties to create a seat riser for my Vibe SeaGhost 130 Kayak. This arrangement worked well, only having to replace ties once or twice. The PVC arrangement raised the seat 42mm.
When designing this I wanted the front of the seat to be a little higher than the PVC riser placed it to make sliding a dry box storing camera batteries under the seat easier. This riser is reversible, allowing me to sit higher (56 mm) for fishing or lower for extended paddling. The low setting is about 6 mm higher than if there is no riser in place. The interior channel is 24 mm to accommodate the seat shaft after removing the end plug.
If requested, I can attempt to make versions with more or less lift.
(Printed with a Creality Ender 3 v2, my only printer, not the Pro that was available in the profile settings of Thingiverse.)