How to self-stitch a 2D rubber sheet mesh?

[ggaliens]

This is how I ended up having to do it.

0) Remove triangles of small area (think with short edges) near border

1) Duplicate and invert the mesh so original and "mirror" are back to back.

2) Extrude Region on one mesh.

3) Weld Meshes.

I think the keys were (0) and (2). I was doing some move faces normal I think rather
than extrude region. And that was troublesome.