I sold my Monster (Had to have a Streetfighter) and I have the tail bag here. It fits perfectly on the rear seat of the Monsters. It has a velcro part that goes under the seat and some ties that keep it secure (also under the seat) It fits a good amount of stuff and doesn't look dumb. Mine is all black and made from the more expensive "Lexel Pebble" material. This is a quality bag and would cost $160 plus shipping plus fabrication time if you ordered it from the maker below.
http://www.luggagelocker.com/sport-seat-sak.htm (http://www.luggagelocker.com/sport-seat-sak.htm)
Mike (NE Minneapolis)
612-701-two five four five
How much are you looking to get for it?
Sorry, forgot to paste the important part :-\ $80