[There was one on the bay a couple of weeks ago, the bracket and a well out of date exstinqisher (2012) went for the buy-it-now of £50 !!!!!!!!!!
I have mine mounted in the boot as you really dont want to be in there any longer than neccecery, if a fire breaks out, let alone scrabbling under the seat for the extinguisher, best to get out, get the extinguisher out the boot, and then decide to fight it or just get clear.