What Ortlieb suggests is to use a "Notebook Sleeve" and storing it, vertically, inside one pannier. It is always better to carry the laptop/tablet vertically so the rattling can be absorbed by the screen frame, and with the battery (which is usually the heaviest part) facing down in order to aid stability.

https://www.ortlieb.com/en/produkt-d...eeve&artnr=nop