Hi Konrad,
IIRC, skins may be created from spline lines drawn internally in the program. Although an actual spline is not output on your screen (instead it will be lines and arcs), there is a rule of splines to observe: sharp intersections create distortions. That is to say, a spline will be drawn, but it will never conform exactly to the sharp corner of your design.
So, if you can fillet the bottom creases of the part, you may be able to make a single skin (somehow). In actual fact, whatever ballmill you use is going to create some kind of a radius corner in the part. But, if the ball radius is exactly the same radius as the final radius on the part, then regretably, the toolpath will have a sharp corner in it, and I don't think it is then worthwhile to pursue a single skin toolpath. If you achieve it, it will have distorted corners.
Its much handier to move on to a solids based cadcam and let it figure out the path. That way, you can concentrate your efforts on designing actual part geometry, instead of guessing about tool offsets, etc.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)