Here is what I did: (Translation: this is just too much work and workarounds for something that should be simple)
Why Did I do all this? Because TC's Rail sweep does not work as it says it does.
Follow along and try not to ZZZZzzzzzzzzz.
1) take the original path, use offset on both sides to get a "fat" path.
2) Close the ends with the Edit tool.
3) Use the split entity tool to break the beziers where they cross. Oops, must explode into ploylines first. Why? Dunno apparently TC can't have anything that intersects itself.
4) Must zoom in almost to the limits because TC isn't smart enough to go beyond one polyline segment to split it.
4a) Delete the intersecting segments.
5) No go back to each intersection, even though we used snaps all the way, and use Meet 2 Lines to get everything together, sort of.
6) Now select each piece and use the Join command to really get it back together.
7) Now we have one polyline. Great, now use convert to curve and we get to play around with the numerical tolerance in Properties to get the corners. Why? Because TC is too stupid to recognize corners of a curve on its own.
I'm sure I forgot some steps.
9) Now we can extrude the shape -- after selecting all the parts.
10) Lest I forget -- now trying to add contour to the shape? Forget it becuase you must select EACH polyline segment OF THE EXPLODED ACIS solid in order to get some shape. I lost it there.
Sketchup or Solidworks anyone?