First off, I'd like to say this looks like a great design, very weight friendly.
1902 has done it two different ways the last two years. In 07 it was flat 1/8" plate with a ton of rivets and spacers.
http://www.chiefdelphi.com/media/photos/26796
Last year it was lots of rivets, spacers, and we flanged the top and bottom of the plates. We did this because in 07 the frame seemed to warp a bit with impacts and what not. It never was a problem because the bumpers are strong enough to support quite an impact, so the bumpers ended up keeping the drive plates relatively sturdy.
http://picasaweb.google.com/DanRRich...00838081699890
However bending the plates, when femed showed an individual panel was much stronger. ( If I remember correctly it was "14x" stronger but the flat plate failed under the loading so take that for what you will. ) For 1902 the verdict was, 1/8" is ok.., but 1/8" with 2 .5" bends are SOO much better. Its not too hard to find a sheet metal break, or a metal fab shop to do this for you, for free, or really cheap. I suggest if your going with 1/8", trying to throw some bends on that bot.