I have been working on this for a while. No where near done but it's at least rideable now.
The seat is hand carved pine. I am going to do something harder this winter but I had never done any woodwork before so I wanted something easy to work with. I did a pretty cool looking ergonomic shape to start with, which not surprisingly really hurt my ass so I had to add padding which I don't like the look out. When I rebuild the seat I plan on routering out a trough to put a piece of steel in as the mount and cover that with high density foam.
I am also going to paint (either Hunter Green or Cream) over the winter, add wooden gauges, light and inlays on the tank.