A good place for an extinguisher is right below the front passenger
seat, front side,  cross-wise, on the seat base behind the passengers
legs....  I have mine there in  a quick-release clamp bracket.  You can
easily reach it from the driver's seat or from the living area (with a bit
less ease)  In that position, you can get to it without going into traffic
should you have a fire after you stop driving and get out..or you can grab
it as you dive out the door to help some other motorist.  It seems to be
about the least obtrusive right there...I never bump it or snag clothes on
it..Handy for a fire outside at a campsite, too...
  Don Hanson