Abstract: A window assembly for mounting in a recessed window opening, especially as the rear window in the passenger compartment of a pickup truck or other motor vehicle, has slidable and fixed positioned panes, preferably right-side and left-side fixed positioned panes with a slidably mounted center pane between them. A mounting frame including a molded plastic, single-sided frame member supports the fixed positioned pane(s) by adhesive surface bonding to a perimeter portion of the interior surface of the panes. The peripheral edge and the exterior surface of the fixed position pane(s) are free of adhesive bonding to the single-sided frame member. The mounting frame also provides an exterior show surface substantially flush with the exterior surface of the fixed position pane(s). The window assembly presents, therefore, an overall flush surface appearance with exposed peripheral edge surfaces of the fixed positioned pane(s).