Is that really the only way to extrude a squarish shape? Talk about the long way home!
Anyway, I tried it and got pretty close, but then found that if I rescale the rectangle after creating the extrusion, it comes apart again, this time along one of the edges.
Many thanks, Al. I'm still not all the way there, but I'll keep working on it.
Meanwhile, if anybody knows a less arduous way to make a square tube, please feel free to share!