i agree with bender ......the dual deck design has many problems....it tweeks easy in first of all and the tension are not distribuitable right in design process.....in the tub chassis design all little curve and is studied to maximize the right tension distribuition and with the modern analysys teqniques all the force-stress sets are simulated and solved correctly becouse tub design has more room to solve the problems ......i think that the dual deck carbon fiber design is in first used for commercial reason (many people would not spend 450$ for a plastic looks car...ok i too :-D) and again in onroad racing if don't make mistake your car will not tweak...in offroad the stress on the chassis are much more at landing of the jumps....so i think that the molded tub graphite chassis is the right choise for the racing application.....see B4 and XX4 as example...
Bye!