Hi Lars, I finally realized what you wanted just after that message - please see the other one above, it shows how to use Blend to put the connecting parts in.

Is that the thing you were looking for?

For things that have a kind of Möbius strip type twist to them, you will probably need to use techniques like that to finish them up. MoI just does not really expect to have a single surface that has touching edges where the "natural" surface normal is reversed on either side of that same edge.

Blend is the general tool to use to create a connecting surface between 2 open edges that have a gap between them.

- Michael