Here is version JR of the script.
A Rail is added, for creating a Ribbon.
One rail is added, without mirror. Mirror can be done manually after the script closes.
A second "outer" rail can be done by re-running the script, with a negative width. Delete the extra copy of the main curve.

Rebuild is good after mirror and/or closure of the curves.

The ribbon can be done by loft, with loft options, or sweep of a line segment, which causes some cross bowing curving or arching.
The solid was generated with a loft, small 3d scale from origin, and two more lofts.

Cross tangent line segments could be done, but loft gets the "same" result.

- Brian

Edit 12/19/2014 Version 3 in post #1 incorporates Join and Ribbon Rail.