well there isn,t too much more to it, but yes its the starting point of making a mould, you would then make a seat from the mould you have made from the template you have created, not impossible but to make a nice job involves mixing the gelcoat / matting/ resin so that it creates a chemical reaction to ensure a strong GRP seat.
Having seen the seats being made last weekend by Triton Seats i would recommend them totally, the quality & finish was superb
andy