Sometimes a little bit is all ya need.
Every firefighter I've spoken to says the best tool in the event of a vehicle fire is a good set of track shoes.
Both of those statements being granted, I like having a fire extinguisher in my vehicle. In the Wrangler world they're handy for putting out grass fires accidentally touched off by catalytic converters. In my Commander world they may be handy for putting out an upholstery fire in the car parked next to mine in the mall parking lot after the smoker dropped his cigar in the seat.
That being said, I removed the panel in the back of the console (there are four clips that hold it in place, easily removed and replaced), drilled two small holes for the mount, used two machine screws, locking and flat washers, and attached the mount to the panel. There is little weight actually on the mount, I had the extinguisher on the floor when I determined the placing of the mounting holes. (Put the extinguisher in the mount, place vertically on the floor, slide against the back panel of the console, draw a pencil line along one side of the mount and across the top. Remove the extinguisher, take the mount off of the console, align the sides of the mount with the pencil line, mark and drill holes).
Obviously not for everyone - and it pretty much removes the center of the back seat from anyone with size 12 shoes - but in my case no one will be sitting there.
A larger one would give more fire fighting capability, but I'm not going to be fighting gasoline or underhood fires - I have good track shoes.
(The pics were taken by a P&S, sorry about the poor quality).