A side skirt assembly for attachment to a trailer of a tractor-trailer, particularly to a trailer frame comprising transverse structural support members extending between sides of the trailer. The side skirt assembly comprises an elongated skirt panel, an elongated support and one or more skirt support members. The side skirt assemble comprises an inner surface and an outer surface. The elongated support is coupled to the elongated skirt panel on the inner surface thereof proximate an upper edge of the elongated skirt panel and extends at least a portion of the length of the elongated skirt panel. The more skirt support members couple the elongated skirt panel to a corresponding one or more or of the transverse structural support members.