I haven't used them backpack style, and am away from home so can't check this aspect of them out right now, but the Mono D80's might do the trick. Rather pricey but I got mine from
www.hellomusic.com when they were on sale there for around $125. Whether they will return there on sale is anyone's guess. If you have the bucks and are in a rush, places like Musician's Friend also have them available, e.g.,
http://www.musiciansfriend.com/acces...ht-guitar-case.