I just finished making one and was simply going to silicone it into place. Figured it would hold it solid and keep it from filling with water in wet exit (rolling) practice and I could still cut it loose and move it if I didn't like it. I clamped two stations to it, used that to get the lines and cut it to shape with a pair of tin snips -- took about a half an hour to make sure the lines were right and 10 minutes to cut. Fits fine and feels quite good. Maybe Shawn will answer -- he also has a fiberglass seat.
good luck
don
: I have been looking at building a custom molded fiberglass seat and can't
: seem to find any reference to how these type of seats are commonly mounted
: to the boat.

: Two methods I can think of are: 1) Make blocks of wood with blind nuts
: installed from the back side. Epoxy these blocks to the hull at the
: locations were the seat would be bolted to the hull. The bolts would be
: near the top of the seat sides and would bolt to the hull just under the
: coaming.

: 2) Mount the seat to quality urethane foam and shape foam to the hull.
: Fiberglass the foam for durability. Use velcro between the hull and the
: bottom of the seat. This would allow for easy seat position adjustment.

: Any other ideas?