[s_forbes]

One thing I would be worried about with this design: It looks like the crossmembers are only attached on their ends. Being c-channels, you would probably see a lot of flex in the whole chassis. It would likely survive through competition, but I would be hesitant to use it.

Since you are designing it with sheet metal, you have the unique ability to make very large structural members that are still very light. Monocoque style construction is something that can be employed fairly easily and will result in a very stiff, very strong chassis.