The other important thing to keep in mind is that you will be changing the battery every match. The battery needs to easily replaced in the pits.
One option from AndyMark:
http://www.andymark.com/product-p/am-0477.htm
our demo bot just has four blocks screwed to the belly pan and a Velcro strap (battery should not fall out if robot is tipped). Also, be careful of sharp metal brackets which might crack the battery during a robot collision.