It'd be interesting to do a survey on vehicle fires. My guess would be 1) electrical, 2) fuel leaks and 3) other, such as a catalytic converter starting a grass fire under the vehicle. Risk reduction, primarily via PM, would seem to be the greatest way to prevent losing your vehicle. A good example of this is air cooled VWs, especially buses. They're known for burning up and the primary reason for that is fuel line failure. Old, cracked fuel lines and poorly or even unclamped lines fail and fuel pours unchecked onto the hot engine.
The take away, in my opinion anyways, should be to insure that your wiring and connectors are of the proper gauge and type and that connections are tight and properly grounded. Fuel lines should be in good condition and properly clamped and that there isn't grease and oil covering parts of your engine bay. Also note where you stop your vehicle.
