Hi Brian, Extrude with Set Path will make what is called a "Sum surface". It's a surface made from 2 curves where all the U direction isoparms will be from the first curve and all the V direction isoparms will be exactly the shape of the second curve.

An extrusion is one example of this type of surface with a line being one of the curves.

I think that I didn't understand properly what you were looking for, I kind of thought you were looking for something like the convex hull around a set of curves or surfaces.

Does the Offset command applied to your path curve give you the side pieces that you need?

Trying to generate a sum surface using Extrude with Set path as in your example will not be good because the result is a self intersecting surface that folds back over on top of itself.

- Michael