In the Tacoma it's in the driver's side rear storage compartment under the thing Toyota calls a rear seat in the Access Cab. In my '95 Tacoma it was mounted to the front of the storage compartment with a metal strap style bracket. A metal fire extinguisher is one of the last things you want bouncing around the cab in an accident. There's a small model mounted to the platform in the back also.
In the VW there's one under the driver's seat and another mounted to the front of the Z-bed near the sliding door.
If you want ot get fancy you can buy vehicle mounted extinguisher systems from places like Jegs, Summit, etc and they aren't that hard to install. I know a couple of off-roaders and several VW owners with them.
Remember your scene safety- you (you're no help to anyone if you're hurt), then your passengers and lastly the vehicle. If you've never attempted to put out a vehicle fire you'll be surprised how quickly it spreads and how fast you expend your small extinguisher- and all extinguishers are small when when you actually have a fire. I would highly advise getting a copy of some firefighting literature on how to attack a vehicle fire or at least talking to a qualified instructor. If you can't put the fire out very quickly then you need to get away from the vehicle. I've never seen one actually explode like on TV or the movies but I have seen things like a rolling fireball that came out from under the vehicle that would have engulfed anyone's legs that was nearby (same way idiots get burned starting fire in trash cans using gasoline- the heavier than air fumes settle then ignite).
Good thinking ahead though!
<--- I've had firefighting classes, but I'm not a certified firefighter.
You definitely have the firefighting lingo down, and as a firefighter, you hit on very valid points. When we talk to the general public about extinguishers, this phrase always sticks in my head. "with an extinguisher, if the fire is bigger than you, you can't put it out". It's a great visual to keep in mind.
If you are on a roadside fire, and using the extinguisher, it creates an immediate cloud of smoke that other vehicles can't see through. Stay off the road, if possible or have someone else stop traffic while you try to extinguish the flames.
All that being said, I don't have one in my truck ;(, but I plan to pick one up today. Good thread