[MTrenk]

There needs to be some sort of structure equivalent to a metal frame. What are safe racecars build out of? Metal and Carbon Fiber.
However, he could be well off with a minimal metal frame, and composite shell.
From my experience, the most effective type of frame is a hybrid of composite monocoque, and metal structure. By replacing bracing (diagonal tubes) with composite panels of equal or greater strength (carbon fiber), you actually achieve a stiffer, stronger frame than either straight metal or straight composite.