This is actually exactly what I am looking at! I found this system that is ingenious! It is just a tube that is heat sensitive. If it heats, it ruptures and releases CO2 into the space where it is running. I could run lines of this in areas that are highly suspect such as the engine compartment, along fuel lines and inside the bus where electricals are stored or cooking is done.
I have reached out to the company to get more information.
As a secondary option, there are systems like BlazeCut that are affordable and easy to install.
I planned to make a spray bar in the engine bay and hook up to a fire extinguisher. Most fires I see happen there especially in coaches. Make sure to kill the fridge pilot and dont let the ole lady cook going down the road and you should be ok☺