Join/merge

Hey Everyone!

This model is really testing me. I am trying to merge/join these two surfaces. I tried using Nonmanifoldmerge which seems to merge it but when I offset the surface to make into a solid it tells me it cant succesfully make it a solid, so i am assuming the fault is at the merging process. Any idea how to merge/join these two into a single and to make it a watertight solid? I am trying to use the grasshopper brep join but isnt working, can anyone help me? I am on a deadline and am trying really hard to figure this one out!!! ANy help would be truly appreciated!!

Thank you!

http://www.sendspace.com/file/pwaml3