Capping problem using Rhino

Hello

I have been using the panelling tools to create a surface of inner and outer wall-lines of tubes/cones. I have tried doing it as as two separate surfaces, (one with the inner walls, one with outer), and as one surface of closed curves making both walls in one.

I have then used ptfinedges to extrude but can't cap between the inner and outer walls to make them appear solid for a prototyping machine.

Does anyone know of a good way to cap in this situation or a better way of making the surface in the first place so that Rhino understands what I'm asking it to do?

Thank you.