Whipped this new seat out this weekend. Started with 2- 2'x4'x3/4" pieces of ply (not sure what type, I went with the nicest lowes had), two hinges from West Marine, little starboard and an old bench seat cushion I had picked up a couple of years ago. The two pieces of plywood were stained with olympia's outdoor waterproofing deck/fence stain to keep them from rotting atleast a year or so. I cut notches out of the seat piece to give it alittle more depth. Hinged up the back, routed the edges so I don't rip my shins up and bolted the cushion on. I also added to little strips of starboard to stop the back from swinging all the way out, which right now it is pretty tight anyway but didn't want it to slip.
Here's the pics.
-Svence