Our team uses bolts. What we have is a "modular" system of cross supports and drive "modules."
http://www.chiefdelphi.com/forums/sh...ad.php?t=85712
Each of the side plates is .188 aluminum (6061 T6 I believe) despite my best efforts to use .125...
The round spacers between the side plates are half inch aluminum round stock tapped with 1/4-20 on each end and secured with 3/4 inch panheads.
The square tubes run from outside plate to outside plate and are 1/8 wall (I keep pushing for 1/16...) with 2 inch long inserts tapped one inch deep 1/4-20 and secured with 3/4 inch panheads.
We have found this system to be fairly lightweight, especially if you use your spacers for axles. In addition to weight, the outermost module can be quickly detached from the rest of the chassis by removing the bolts in square tubes. For wheel/chain repairs, you can simply remove the outermost side plate.