Hi Gunter, one thing to watch out for is that your model has an area of it where the surface goes into a very tight bend across a short distance:
Surfaces with very tight bends in them like that can be generally problematic for shelling, especially to the inside of the bend. The offset surface will tend to bunch up and cross over itself in cases like that. Any self intersections in an object can potentially confuse the slicing mechanism that the 3D printer prep software will be doing.
If you run into that it you may need to manually make an interior surface doing another loft or sweep similar to how you did the outer one rather than using Shell on a shape like this.
Thanks for this. Yes you're right there was an area with an overlap. I have a Flashforge Finder 3D printer and, oddly, it printed surprisingly well, although I'm still refining the shape.
Gunter