Thanks - I've been curious about Sketchup and this describes it really well
A little off that subject, putting a vestibule on the mid works really good. When there's a zipper down the center of a side panel, there's tension across the zipper - it's hard to zip it all the way down. When the zipper is on the ridge of the vestibule, you can lower the zipper down easier. And I think it's easier to get all the ridges taut, especially if the site isn't level.