Upper and lower window track strips each define an elongate panel receptacle of generally rectangular configuration for receiving an edge portion of a structural panel in tight fitting serration retained relation therein. The upper and lower window track strips define wall structures forming a pair of upper and lower window guide tracks, respectively, thereby allowing a pair of window panes to be moved in sliding fashion between the upper and lower guide tracks to open or close the windows. The upper window guide tracks are deeper than the lower window guide tracks to permit the window panes to be moved upwardly and laterally for removal. Rainwater collected within the lower guide tracks drains at the ends of the lower guide tracks or via drain holes therein. The lower window track strip is provided with a resilient cushion strip to protect objects such as guns, camera lenses and the like that contact the lower window track strip.