Seems simple, on the surface

Hello;

I would love to hear some advice about a quandary I'm having.  My goal is to create a shell (expression not the modeling feature) for a cargo box.  The origional is fabric and so my intent is to use surfaces to model the thin feature. I created several 3D sketches and have the points laid out.  But every type of surface that I attempt produces errors.  The only successful surface that I could produce was a lofted surface which didn't line up at the point farthest from the origin.

Any advice that you have is appreciated.

SolidworksParts And Features