As with many things, the answer to these questions is - it depends. What is the temperature of the room you keep your snakes in (think highs and lows for the entire year)? What about the humidity level where you live? Yes - adding moss to the inside of a hide (creating a "humid hide") is something that can be effective.
You're starting to think along the right lines here. Keep up this thought process and your snake(s) should be well cared for.