The most common method for senior body construction is laminated wood strips covered with fiberglass. There are several techniques you can use to get your wood strips to form the shape that you want for your racer. Lay your floorboard into the bottom shell, level, and fiberglass into position.
Optional method requires more floorboard shaping.
Remove the body from the formers. Lay you floorboard into the body, level, and fiberglass into place. Fiberglass your two body halves together. Laminate part way around. Knock interior formers out when done.