if you're exposing for the car and the model is right beside it, it shldnt be much of a problem, but a flash is definitely not bright enough to light up a car, not nicely perhaps, only a mere portion of it.
i suppose if the car is exposed properly, so will be the model. under the right exposure nothing can go wrong, right? haha
another way is to try light painting? long exposure and painting with torch lights since you all have powerful torches. i'm not sure on that but that might be useful, and you can give diff lighting to the car bringing depth and 3d feel.
just my thoughts, not exactly confirm tips.
