An electronic equipment enclosure includes a frame structure and a customizable side air dam kit. The frame structure includes a front frame, a rear frame, front-to-back frame members connecting corners of the front and rear frames together, reinforced bracket structures located near ends of the cross members, and extruded horizontal mounting rails parallel to, but inward from, the front-to-back frame members. The ends of the horizontal mounting rails are connected to the reinforced bracket structures. Panels are installed in longitudinal slots in the front-to-back frame members and horizontal mounting rails, each of which is extruded. The customizable side air dam kit includes a framework of horizontal and vertical frame pieces, adapted to connect to the frame structure, and a customizable air dam panel supported by the framework. A plurality of the frame pieces are provided to an installer for use in constructing the framework to fit the specific frame structure.