I think V2 is the right way. and much simpler than working with curves. And it worked.

I think the Problem is not the construction afterwards, it’s the initial mesh.

(right=initial; left=constructed)

You got some not nice edges and triangles. And becacuse you search for the closest Points to Surface boundary, you get These triangles afterwards.

This will be fixed, when you plug the delaunay right in deconstruct mesh:

Now it still Looks weired, but that’s because you moved the boundary verticies up, und beneath there is a “quad” strcucture, so when moving one of them Points, you get some edges like on the Picture.

If you want the mesh to be “extruded”, so the walls have the same “boundary” at top and bottom, you could filter for the naked edges, Project them at your top curve, and create “new” meshes out of it.