I'd really like to know more on this topic.. like what kind of fire extinguisher would be good to mount in a car, or at least include with my kit.
There are brackets that attach to the passenger seat bolts, so you wouldn't have to make any extra holes.
http://www.thebracketeer.com/
https://elementfirecanada.com/products/seat-rail-mount
Looks like the Element is a rebranded Fire Safety Stick, recommended by Nicky Grist. I think I'll get one of these. I'd get two if we made a group purchase.
Some related discussion by another WSCC: https://forum.wscc.co.uk/forum/topic/139240-fire-safety-stick/