An actuator is adapted to selectively extend and retract a bumper member, the actuator is mounted at least partially within a tubular frame rail member of the motor vehicle. The main frame rail member may be of a standard length or of a shortened length. By mounting the actuator inside the tubular frame rail member, the bending stiffness is more effectively impacted by the outer tube of the actuator. An additional tubular frame rail member is optionally attached to the main tubular frame rail member. The actuator is mounted at least partially within the tubular frame rail member and at least partially within the additional tubular frame rail member. The wall thickness and cross-sectional shape of the additional tubular frame rail members may be adjusted to obtain a desired bending stiffness including the effect of the outer tube of the actuator.