Recently I have been looking at how people are mounting fire extinguishers in our cars without cages. I think the seat mount by Brey-Krause as seen here is really slick, but quite expensive. I haven't seen anyone mention a similar alternative by a company called vetteworks. They advertise one of their seat mounted brackets as fitting fourth gens. Of course we all know that 4th gen seats are the interchangeable with third gen seats so I ordered a chromed 2.5lb Amerex halon extinguisher and the bracket from them.

More pics. Your passenger still has enough room to sit down, but they just have to be careful not to kick the extinguisher when entering and exiting the car.