My rack is open on all sides (though, one end faces the wall), so I supply all of my snakes with hides. I suspect I'd do that even if I had a rack enclosed on three sides. To me, they seem to like not only darkness but feeling secure, i.e. feeling crammed into a small space. Plus, my "hides" are typically 6 quart tubs with a hole cut in them. I can easily put some moist towels, moss, etc. in the tub/hide when they shed.