How to model mounded surface with curvature in 2 directions...

Hi All,

I have been trying to model the back of a new phone case and have tried a multitude of different lofts, cuts, and extrusions.  I've got something that is okay, but not as clean as I want it to be (see the attached zebra stripe image). 

There needs to be curvature in both directions when looking at the side of the case (see attached images 2 and 3 below).  Similar to the HTC phone back shown in the image below.  Any tips on how to do this cleanly?

http://images.anandtech.com/doci/6455/HTC%20Droid%20DNA%20Hands-on-24.jpg

SolidworksParts And Features