Abstract: The present invention is directed to mounting frame assembly for mounting one or more window and/or doors in an cut-out portion formed in a body panel of a vehicle, such as a truck or camper cap. The window mounting frame is shaped to fit around an edge of an opening formed in the cap. The window mounting frame has a clamping surface formed thereon. A clamping element is engaged with the clamping surface to hold the window mounting frame securely within the cut-out portion. The clamping element holds the window frame to the cap by frictional engagement of the cap wall between the inner face of the outer periphery of the cut-out portion and the clamping surface.