Joint exterior and interior surface to a unique closed surface


I am using Rhino in order to close this complex shaped cylinder. However, i can not find a way to join the external surface (gray) and the internal surface (purple) to the blue one directly. When I try surface by sections, the surface gets twisted, even for gray to blue.

If anyone had this issue, do you know what tool to use ? I tried several of them in vain.
Thanks in advance,
Théophile Kurtz