If you're shooting for a true-to-stock finish, basic undercoating was then applied to all chassis pans in the following areas: one or two passes up the length of the trans/driveshaft tunnel, crosswise across the high rise of the floor in front of the fuel tank (area over the rear axle) from wheel opening to wheel opening, and finally in all 4 wheel openings. This was the bare minimum,from the factory. If a dealer could up-sell it, the entire floor pan could have been undercoated; not uncommon in northern climates where salted roads could wreak havoc on chassis.