There are a lot of teams I know of that uses 4x4 aluminum box tubing for their chassis. Back in 2007, I talked to Karthik and he directed me to Taylor. They were gracious enough to share close pictures of their chassis. Personally, I love 6wd and in my designs I use an 1/8th inch drop. Below are few pictures that may help you.
http://www.chiefdelphi.com/media/photos/27523 ... that's 1114's 2007 chassis
http://www.chiefdelphi.com/media/photos/29996 ... that's 1345's 2008 chassis
http://www.chiefdelphi.com/media/photos/26373 ... that's 1345's 2007 chassis
1114 makes their own plates and puts the transmission inside the box tubing. It's very neat. If you have any questions, I would suggest getting in touch with Karthik and I am sure he will be more than happy to share their designs. Also, if I can be any help, you are more than welcome to send me a pm. Good luck.