I have a 3.5 pound Halon extingusher in my Westy in the traditional
place by the B passenger pillar. Not cheap, but I figured there is
nothing better and it won't leave a residue (and hence should I ever
need to use it, I have hopes of preserving my fine Westy.)

I also have a 9 pound Halon extingusher, but that's mainly intended for
my house.

Somewhere around I believe I have another (older) 3 pound one that my
brother gave me a couple of decades ago, after my one (and only) engine
fire destroyed my 71 Super Beetle.