I'll be curious to see what those who have a lot of anaconda experience say to this, but in my own experience, and from what I have heard as well, anacondas tend to easily develop skin problems from too-high humidity. I would think that a cage with a relatively lower ambient humidity, coupled with a high-humidity box so that the snake can "hygro-regulate" (made that word up just now but it works, don't it? ) would actually be a good thing ...

As I said that's my limited-experience opinion; I'm curious to hear what more experienced folks have to say.
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-- Kitt