How to create a rectangular pipe between gap surfaces

How to create a rectangular pipe between gap surfaces with consistent thickness along the entire length.
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“between gap surfaces” meaning you already have two surfaces?

That’s potentially pretty easy: loft the edges of each side. Getting the edges to loft may require a little tree management, but otherwise super easy.

However, if the surface edges have inconsistent distances from each other, you won’t get the perfection you’re looking for because it’ll be geometrically impossible.

Can you post a .gh definition to show us where you’re stuck?