A window or door with a radially extending metal or vinyl casing flange mounted in an opening of a building having vinyl siding is protected from hurricanes and other violent weather by providing a panel having dimensions greater than the opening and bracket receiving slots; and a plurality of L-shaped brackets having base plates and perpendicular mounting plates. The bracket base plates are inserted between the window flange and the vinyl siding and secured to the building with fasteners, which are inserted into a wooden frame surrounding the building opening. The panel is then positioned over the opening, with the mounting plates inserted through the slots. The panel is secured in place by temporary fasteners, such as cotter keys.