Fumigating a car is a lot more difficult than fumigating an entire home. There is a lot of small, inaccessible space. Moreover, insects could also find their way into your seats and pretty much camp there until your whole car is full of bugs. If you really want to get rid of every single bug in your car, the best course of action is to call a pest company. They'll deal with the bugs in your cars, similar to what they'll do with a house. They'll fill up your vehicle with pesticide and seal it up until all the bugs in your vehicle are dead.