A strut assembly for mounting an aerodynamic fairing assembly for attachment to a trailer of a tractor-trailer having a centerline, transverse structural support members extending between sides of the trailer, and longitudinal members extending along a length of the trailer. The strut assembly may comprise a mounting plate, a strut body, and a substantially rectangular composite spring. The mounting bracket comprising a mounting plate and a pair of spaced apart sidewalls. The strut body rotatably may be coupled to the pair of spaced apart sidewalls on the mounting bracket. The substantially rectangular composite spring may be coupled to an upper surface of the strut body and configured to contact an underside of the mounting plate of the mounting bracket to resist inward deflection from an external force applied to the strut body.