I made some steel brackets for the seat and glass fibred them into the side pannels. never had a problem since. Maybe you could try to not do the bolts up tight, that would allow some flex.
Cheers
Ian

i had same problem with mine so cut off the broken parts and used velcro on bottem of seat stuck on with superglue and on the subframe to hold the seat in place,also ideal to get at battery as just pull seat off

nibot6 wrote:i had same problem with mine so cut off the broken parts and used velcro on bottem of seat stuck on with superglue and on the subframe to hold the seat in place,also ideal to get at battery as just pull seat off

I'll do the velcro because I'm sick of the smell of plastex, just have to powdercoat the subframe first.

i did similar to what morespeed did, i bent alu brackets to fit expoxy + fibre glass to finish it. been over a year now with no issues.