Where all to undercoat in the front fender wells?

I was told by 2 different Mopar fanatic friends that the insides of the front fenders were painted body color. Then a factory worker took a special gun for this purpose and sprayed a special 3M coating (not undercoating, but a coating with resilience for absorbing rock hits) across the top inside of the fender. The gun sprayed a rather sharply defined band. I don't think it was even capable of spraying the whole inside of the fender. I think they sprayed coating on the fender liners also. One friend of mine owns the gun, tank, and material . The material costs $100. If someone needs to know, I can get more details.