Get some boric acid and mix it about 1 part to 6 parts sugar, dissolved in water. Use something like an old pickle jar. Get some cotton balls and dip in the solution. Take a margarine tub - 2 from what you describe - and punch holes around the bottom for ant access. Place in their trail(s) inside the car. You can accelerate things a bit by taking damp sugar with your finger and smear on the holes, so they'll investigate sooner. They'll enter, snip off pieces of the poisoned cotton and take it back to their nest, wherever it may be, and poison the other ants and the queen. It'll take a few days, but they'll be gone. (BTW, this works in houses also.)