A vehicle rocker assembly includes a sill outer and a sill inner that together define an elongated hollow interior. The vehicle rocker assembly also includes a rocker insert disposed within the elongated hollow interior. The rocker insert includes a stiffening member defining a wave-shaped structure and including at least one sheet defining a fore edge, an aft edge, a first side edge, and a second side edge opposite the first side edge. Additionally, the fore edge and the aft edge are disposed at different locations along the length of the rocker insert. Moreover, a crest of the wave-shaped structure extends between the first side edge and the second side edge and is configured to carry a load path laterally between the inboard and outboard wall portions.