Update on this: the Mask is working, and I set up the ScrollRect as per this thread, after some confusion. It's working with the Unity Text component but not with STM. The sizeDelta.y of both the Content wrapper object and its Text child remain at 0, even as the STM bounding box grows bigger. I can work around this by manually setting the Content's sizeDelta to match the bounding box, but I'm guessing this isn't expected behavior.