I've got a 10lb CO2 tank (for tires not fire) mounted to my drivers side roll bar using a Powertank bracket and Hose Clamps. Super nice bracket and not much more than the cheaper QD mounts shown here. May be worth looking into if you want a premium solution.

ETA: http://www.amazon.com/gp/product/B00...2B9ZM8KCA61HMZ

 

I see these on a lot of ULTRA4 race cars... a little spendy, but a little more refined.
Good luck!

Black ORS Quick Release with Billet Cage Rings | Off-Road Solutions

 

I get all mine form JP5 Engineering

 

Very nice looking rig!

 

Attached to the side of the drivers seat

 

Mine is secured with Quick Fists on my Vector MP Table.

 

Mine fits perfectly between the driver's seat and side molding. It snug without any movement so I didn't have to buy any sort of mount. I really like this location because its within immediate reach.