Here is Team 1345's 2007 Chassis. Kids wanted to have a low ground clearence chassis and 6wd. We used 4.5"x4.5" box aluminum tubes for 2 modules (on the side).
In this case, we were inspired by team 1114's prototype chassis. All we needed was some 4.5"x4.5"s. It is 37 inches long and 27 inches wide. The C channels you see are 4.5"x4.5" cut in half with a notch. There are L brackets that connect the C channels to the modules. One side of the L (the side that is connected to the module) is riveted on with .25" steel rivets, the other side is bolted on with quarter inch bolts. We ran a single #35 chain through each module and used a vertical tensioning system. The final product weighed 53 pounds (including electronics).
Here are some links to pictures of the modules and the chassis. If you have any questions, or would like to discuss, feel free to send me a message.
http://www.flickr.com/photos/7634503@N04/444303299/
http://www.flickr.com/photos/7634503@N04/444303297/
http://www.flickr.com/photos/7634503@N04/444303281/
http://www.flickr.com/photos/7634503@N04/444303255/ (last minute cheeseholes).