What fire bottle system to use?

to cover the areas it will not be small period. You need a 5 liter or 10lb bottle best AFF which is water based. It makes a mess but prevents some fire reignition and is not good for your interior. AFFF has a cooling effect on your body so that's good. "Wet" is controversial in fires. they help prevent some cloth from burning but yet wet makes steam in firesuits and you still get cooked. That is one of the big reasons for using carbon-x underwear instead of nomex. Nomex is best on suits because it is not only fire resistent but tough. Carbon-x is fire resistent and does not wear well but wicks away water that can steam burn you. You can use halon but there is reignition issues and leaves zero residue. Halon also has haz mat charges and difficult to get rechargerd or recertified which is required by some race sacntioning bodies every 2 years. You can use a "firecharger" or ESS system which is AFF based and user refillable and powered by a large CO2 cartridge. I think I know your casual use so this may be the best system. Be careful of old firechargers or ESS on ebay. New units have a special cover to protect the CO2 cartridge that sits on top from getting hit and bent causing the unit not to work and yet give you no warning. In your streetcar the perfect place to put a system to be functional but out of the way is the front bonnet where the tool bag is. Then you can plumb through the firewall to the interior and then again through the firewall to the engine. Don't buy used firesystems or used parchutes.