A method for manufacturing a lower body component for a vehicle is provided including forming a one-piece floor pan at least partially defining a vehicle passenger compartment and substantially extending longitudinally at least the entire length thereof, and forming a one piece reinforcement structural member for reinforcing the pan. The method also includes simultaneously forming the pan and one-piece reinforcement structural member by stacking a pair of weldable sheet metal blanks sufficiently close together to define a comon interface, positioning the stacked blanks between moveable profile forming dies, heating the dies so that the blanks reach a superplastic forming temperature, and plastically deforming the stacked blanks into a lower body component having the profile of the dies. The method also includes friction stir welding of the stacked blanks at the common interface.