Extrusions twisting/bending Rhino

[Thunderhead19]

How do I lay out the true lie of an extrustion bent to fit a twisted surface (hull plate). If I just arbritrarily tell my Rhino software what line I want the extrusion to follow, I don't think I get a "true" representation of the extruded channel I want to use. I don't want to maintain the original cross section, because when I twist and bend it, it really does change, but I can't see how to control it so I get to the real.

[Fred2]

I use sections to do this for example every 4 frames draw a setion of the profile "perpendicular" to the frame, once is finish extrude using 1 rail (wich is the one that is laying on the hull surface and defines the path of your longitudinal member) and then select all this profiles that "follows" the curvature of the hull.

i hope it helps