[s2xr2]

I am hoping to start motorsport this year with some hillclimbs/sprints and therefore preparing my car. My question is:

What is the best (safest?) way to fix a bottom fixing seat to the car shell?

I need to keep it all FIA approved and wondered what method is best. I have been suggested a few:

1) Use the original or substitute runners (but neither quite match exactly and will need hacking, is it an FIA approved method)
2) Fix it to the shell and bolt through the floor (but is this really safe in a crash, also does the bolt holes need reinforcing with sheet metal)
3) Weld in two metal box section runners between the sill and centre tunnel, then bolt seat to these (any comments on thickness and section size e.g. 20mm x 10mm x 3mm)
4) Fix it to the Roll Cage

Any help would be appreciated.

S2