letterbox

I am looking for a Letterbox draught excluder but my Letterbox is in a wooden door with glass and its small. The appature is 21cm Wide by 6cm high. The bolts that hold it on are with square nuts on the inside of the door. Any ideas size wise? Thanks

Anyone have any idea on whether it would be safe to cut out a section of the front wall in an archway to insert one of these letterbox options? Veritcal: http://www.lettasafe.co.uk/16/LS17/highway-through-wall-letter-chute/product.php Horizontal...