I definitely keep a water dish in everything I hibernate. Cold air is dry. Heloderms in general dehydrate easier than you might imagine in a dry environment. They spend 95% of thier lives in cozy dank burrows that stay relatively humid bro and gilas n beadeds become very active after rains.

I live in So Colorado so its really dry here but I would still keep a water dish with them even if hibernating in a humid area....if nothing else I'd bet ya notice they sleep up against it sometimes absorbing water that way some and it will maintain a healthy humidity in the cage/box too.

peace