Well I have been in pyrotechnics for 17 years

yes for 17 years. And only in the last 8 years I finally figured all the things out by joining clubs. Passfire "making big fireworks" and also into making Pyrotechnic flash cannons for stages or flaming boxes "which uses propane and oxygen" or a bottle of propane, which fills an empty propane bottle that has it's safety float removed, which in turns get pumped into the box with an pilot flame "which always dies, hence the stun gun". The reason I suggested adding a oxygen bottle is because it will give you a 2-3m flash flame

, and will make it safe to drive with. Hide the nozzle behind your mud flap, or drill a small hole at the bottom of your car's frame. Paint the outside of the nozzle the same colour as the surrounding part, as well as the wires leading to the nozzle, also make sure that it is insulated and far away from each other, just make sure the bare tips come close to each other.
PS: electronic gas solenoids are a bit pricey as you would need two for the system to work.