Sounds like you have a hole approx 20" x 4", or something near that. If it were mine...I'd go to Lowes, hardware dept, and get a piece of diamond plate aluminum, cut it oversize to cover the hole. Round the corners, smooth the edges, and use buytal tape to attach it and then drill and attach permenantly with screws. Tape will water prof it. Now you can mount any type of light to the diamond plate. Even paint the diamond plate to match rest of siding.