Rectangular tubes?

I was trying to create a ruled surface using wood of a rectangular section, that should look like the first image. I tried with rail in Grasshopper, but it didn't work although I gave a line path and a section curve.
Finally I created 2 section curves and lofted, but I am still wondering what was wrong with rail...
Or would there be any other faster way of making rectangular tubes?
Any hint is welcome.

Thanx