It was difficult to find a place to mount a fire extinguisher in my jeep, but this is the end result.  Basically on the roll bar above the back seat passenger.  I decided on the driver side so it would be easier for the driver to get to it.  I went with a polished aluminum mount made by ‘drake’, with the steel pipe clamps.  It is super solid and will not fall off.  Its mounted at a slight angle to keep it below the top of the roll cage.  For those of you who do not know, when you go off roading events, they commonly do safety checks (of each vehicle).  A fire extinguisher in each vehicle is a fairly common requirement.  (along with a first aid kit, roll cage, seat belts, working 2 way radio, full size spare tire, …)