Don't have a photo handy but the standard spot is in front of passenger seat. You just need a flat piece of aluminium that runs between the bolts that secure the seat rails. You then attach the extinguisher holder/bracket to the aluminium bar. The seat will still be able to slide over it. I got Maximum Motorsport to fit mine but if you have a workshop handy its easy to make one up.

Note that if your going to do any CAMS sanctioned trackdays you'll need the extinguisher holder/bracket to be metal and the extinguisher certified and stamped. I've seen a few people get caught out by this recently.