Extract Mesh Naked Edges

I have two complex surfaces that are being Delaunay meshed as top and bottom. I need to close them to compute its volume. 

To complete this task, I need the edge curves / vertex points to mesh the sides of the volume.

Going FaceBoundary > Boundary (mesh to NURBS is computationally heavy and would like to avoid that since I have around 8,000 thousand panels.)

Mesh Naked Edge gives me points even after I Join Mesh > Weld etc. - I dont get it, Where is the Naked Edge

Please advise the best course of action. 

Thanks