yes you want it as light as possable, just get i light weight battery, that will save a few pounds.
and if you realy want to stiffen that up all you would need is a steel or better yet aluminum plate that conects the two towers olny 2-3in wide, you can make the ends a U shape and bolt it right to the top of the shocks.
now after my own addvice on how to make one can someone please tell me how theys towers would brake? i know it is possable beacaus my 87 325i parts car has a very, very welded back together rear pasengerside shock tower. i cant figure it out