I recently added a small Philadelphia tub with a hole cut in the side and filled with sphagnum moss. The plastic is thick enough that the edge won't harm them on the way in or out, it's certainly no more likely to harm them than the edge of a rock or a the edges of the logs they slither over. That's sitting in the checkered/blackneck viv permanently now. As I don't press the lid tight I can just lift it to see if anyone is in there and to keep the moss moist.

So far Binky has shed perfectly every time, the moist hide is there more for Bethan's benefit (she's never shed well).