I missed a few photos during the process, but here is a quick recap.
I made a seat pan out of a 1/4" thick piece of pre-made fiberglass, courtesy a scrap piece of an anti-flotation flange from an AdvanTex AX20 pod (p00p cleaning box):
Another views, showing the front and rear mounting brackets. the front brackets pulls double duty, as the rear mount for the fuel tank:
I used foam crafting blocks glued above and below the seat pan. This is where I started shaping the foam with saws and sand paper, but failed to get any pics:
I managed to snap one photo of the seat with the first layer of fiberglass cloth applied, before I put on the rubber gloves and got covered in resin:
I've since stripped the form off the lower foam blocks, and have it sitting in the sun to fully cure. The rear hump has the foam encapsulated with cloth, so it should be fairly robust. In a few days I'll turn it over and add some fiberglass matting material to the lower side pieces, to give them a little thickness. Then I get to spend countless hours getting it smooth.