Yep - started planning with a single "tower" instead of three separate cases to ease layout planning. And your divider idea gave me an idea to put additional 1U rows to separate cases from each other! This way it looks like the real deal.

Still - it would be awesome if I could lock certain rows and try to "optimize" the rest. And yesterday I came with an idea to have "groups of modules" - so that I could group some modules together and then move it as one group. And if you'd organize automatically - it would respect this group without separating the modules.