I think one thing to watch out for is mold. Most of my snakes only get their moist hide put in when they go blue- and then they mostly stay in the hide without moving until they shed, and then maybe a day after, if I don't remove it right away. Then I take the hide out and remove the lid so it can dry- and if the moss is moldy, I replace it. I have tried paper towels, but the snakes don't seem to like that as much. One of my snakes (a cali king) loves his moist hide and goes in it a lot, so I leave it in with him full-time. He also really likes to sleep under it- he must like the super-confined feeling and the cool plastic right on top of him. My moist hides are disposeable tupperware things with a small doorway cut in one side, at the bottom. I've seen them with the door on top, too.
Why did you think your Westie needs a humid hide- for shedding, or something else?
Nanci
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0.0.1 Normal Corn, 0.0.1 Cali King 0.1 Nelson's Milk
0.1 Tricolor Hog, 0.0.1 Eastern Hog, 1.0 Eastern Box Turtle
0.0.2 Desert Torts, 2.0 Feral Pigeons