Moisten the moss, and squeeze it so it's not dripping, but damp. Leave a hole big enough for your snake in the top. I've used a humid hide on both the warm and cool sides (b/c of the way the different tanks were set up), but the warm would be better.
Moss would probably be better for the humid hide than the coconut husk bedding. I use moss in the hide, and then the coconut husk mixed w/aspen for a couple of my tanks that I have humidity issues with.

Just be sure to check it regularly. If it starts getting moldy, or he's used it for a potty spot, the moss needs to be thrown out, the hide cleaned and new, damp moss added back in.

R