I've not tried, but I'm familiar enough with modern CAD software to know how I might approach the problem. Basically you draw your cross-sections as NURBS curve

I've not tried, but I'm familiar enough with modern CAD software to know how I might approach the problem. Basically you draw your cross-sections as NURBS curves, then let Catmull-Clark subdivision make a smooth surface. I find that much easier than using a pencil.