So I didn't want to sacrifice portability by adding on a $30+ neoprene sleeve. The Air itself feels pretty study. It is, however, not waterproof. So I've been looking for a tight fitting 'case' that would provide water protection with a bit of surface protection.
Something like a .... baggie (I know what you were thinking).
For the moment I'm using the Ziploc 2 gallon Heavy Duty freezer bag: 13" x 15.6". The horizontal (13") dimension is a good fit, but it's far too long. I would prefer a 13" x 8" baggie. So I'm still looking, but for the moment the current bags are fine. Those I don't use up on the Air I use in the kitchen. The price is certainly right.