if the chassis is made from 5251-H22 aluminium and is unsupported between the steering bulkhead and the batteries then I wouldn't be at all surprised. if that material spec is correct (from the CML website - link below) then IMHO it's totally the wrong material....waaayyy too soft for the application. it is cheaper than 6082-T6 aluminium I suppose and is easier to bend (from a manufacturing point of view) but an incorrect material choice for this design.
http://www.cmldistribution.co.uk/new...iew=0000001811