A rocker panel assembly for attachment to a vehicle, comprising a rocker panel body, a first end feature situated on a first end of the rocker panel body, and a second end feature situated on a second end of the rocker panel body. The rocked panel body has an outside surface generally presented in the form of a convex surface, and an inside surface generally presented in the form of a concave surface. The outside surface of the rocker panel body extends outwardly of the vehicle, to present an outboard section having a predetermined profile based on targeted aesthetic/performance characteristics. The inside surface of the rocker panel body has at least one transverse rib positioned therein, the transverse rib being arranged generally perpendicular to the longitudinal axis of the rocker panel body.