The Sonex seat is very light, very clever, and very much a PITA to install and remove. I need the wings on and off and on this airplane before it flies, so I have no desire to put the seat in at this time, but it's also a PITA to try and work in the cockpit without one. This temporary version is 1/2" ply bottom and 1/4" back, with a Hardware Store piano hinge at the junction. The foam "tractor seat" makes it bearable to sit on.