I have a Knog messenger bag/pannier with a padded spot for a 15" computer. I've been using it for years and never had any problems with either a Lenovo or my current MBP. The biggest problem was that as a pannier it only attached at the top and wasn't secured at the bottom to the rack, so I've used a bungee cord to keep it stable. I just had a thread about looking for something new but upon inspection of a sample of panniers at REI decided that what I have is really what I want. It is by far the cheapest option I've seen too. Knog Franks Dog bag I don't think this listing includes the pannier conversion gear, just the bag.