Waterproof case for Macbook Air

I want a robust, slim & waterproof case for 13" Macbook Air. If it has storage for a Magsafe power adaptor and a few files then that would be perfect. Does anybody have any suggestions? I l own a Thule Gauntlet Sleeve but the velcro strip has pulled off, apparently a common fault, and I have lost faith in the product. Thanks for your help