My 1991 Bigfoot
17 has a boss, a bump, in the door frame, below the holes for the door lock. This bump is only in the center of the frame, with a flat frame area inboard and outboard of the bump. Sorry, I am not at home so I cannot provide a picture. A spring loaded roller is attached to the edge of the screen door. It rolls across the door frame when closing the screen door. When the roller passes over the bumb its spring is compressed. After passing over the bump the roller springs back against the flat area of the frame. The boss then keeps the screen door from opening until you push on the door. This arrangement has come from the factory.
On mine the screen door opened separately from the main door, which can be a nuisance. The small steel plate on the screen door was not flush with the magnets attached to the main door. After shimming the magnets to be flush with the plate, the screen stays with the main door when opening, unless you pull them apart.