Need Help With Sheet Metal Designing

[JTN]

I've become really interested in sheet metal designs over the years of watching FRC competitions and looking at the robots compete. This year I finally decided to start working on a CAD model for a swerve-compatible robot frame that is lighter, takes up less space (or takes up different space so we have more room inside), and more aesthetically pleasing than our current (and past) frames made of Item (similar to 80/20). At the moment we have no engineers who know much about sheet metal, but we do have CNC mills (I know they take a while) and the proper equipment to bend large quantities of metal. What I need help with is how to actually design a frame and/or components and how to attach the parts together. So far all I have been able to come up with in terms of attaching parts is this: https://docs.google.com/file/d/0B9fw...it?usp=sharing
(Sorry for URL instead of direct image. Still have to figure that out.)

All help is appreciated. Thanks!