I use IDEE Anti-Shock Sleeve for my Macbook before I throw it into the Ortlieb pannier (or whichever pannier I happen to be using at the moment). Works great. Best protection I ever bought for any of my laptops. I have the 13 inch one and a 15 inch one.
I like the flexibility of using a sleeve like the IDEE, so I can use whatever bag or pannier I want.