If I follow correctly, we're looking at 3/6/9 square tiles for corridors plus some turns and junctions. Then put the overlays next to them and generate a map with just overlays and corridors? This is a different line of thinking that I originally intended, but is easy enough to do. [My GM wants whole maps with overlays. But if I'm making whole maps and overlays, I might as well break them up and add some corridors.]

Is this generally what you are looking for?
Corridor (3x2).jpg
Corridor (6x2).jpg
Corridor (9x2).jpg
Corridor (12x2).jpg