CO2 will just narcotize the cockroaches and they will wake up when it is gone. Use permethrin (Sawyer’s tick off) to spray the interior of the car…harmless to humans but death on all arthropods. Or, get some mouse glue traps (the roach motels are too small to hold these large roaches)…they will be hungry and will come and get stuck, and then you can just toss them in the trash.