To understand the intent,,,,where the fire is most likely to be is the engine compartment. At speed its a high pressure zone, you are in the passenger compartment, low pressure. Trouble travels from high to low pressure,,,so be sure to completely block is route. Anything,,,fuel,oil, coolant{which will be hot}, is gonna try to get in the drivers seat with ya. But if its turned to fire,,,,,going from high to low is kinda like a cutting torch. Its gonna come in and make the hole, and the fire bigger as it does.
Electricians use "FIRE CAULK", to create a fire stop where the wires go from floor to floor, But its sometimes hard to find locally. For small gaps I've used muffler sealing compound that comes in a toothpaste sized tube, and can be found at any parts store. Seal it good.Fire is BAD.
Good Luck, RICK