Tony,

A solution was suggested to me that worked a treat. Buy a sheet of aluminium (I got mine from Bunnings) that was about 600mm x 400mm and 0.6mm thick.  Remove the allen head bolts on the front of the passenger seat rail and loosen the rear ones.  Measure and cut the width of the sheet to be just wider than the seat rails and then drill holes so that the original bolts can go back in.  This creates the base to then screw the metal fire extinguisher mounting plate to.  To avoid it bouncing around mount it so that you can slide the passenger seat forward until it rests against the extinguisher.

The 2 things I liked was that I didn't drill any holes in the car itself and when you are not using it you can remove the extinguisher bracket and have the aluminium plate underneath the floor mat (I trimmed the sheet so that the mat clips could still be used), ready for the next quick attachment.

Enjoy the track in your GTV. I did the same as you last year.

Hi Guys
I understand that people don’t won’t to drill holes in their cars and this does sound like a good way round but I’d look at the strength of the material you are using. There is a reason why metal brackets are specified so screwing them into .6mm aluminium is probably not the safest option.  The same concept can be utilised but I would look at using at least 3mm aluminium and make sure you use nuts and bolts rather than self tappers.  While aluminium is a great material it fatigues very easily the last thing you want is a 1kg fire extinguisher flying around the cabin in a roll over situation, just something to think about

Sorry i should have specified. Im using galvanised steel. Im not exactly sure of the thickness but it would be 3mm or more and its pretty strong. I was talked out of aluminium for the same reasons.