It's better for the snake to spend longer periods of time at the cool end - most of mine choose to, anyway. It's actually overheating that's more dangerous. I'd go with putting it on the cool side as well.
Yess, the moisture will slowly evaporate. You'll need to keep it moist by re-wetting the moss now and again.
Just make sure that your snake doesn't spend all its time in there, as being damp all the time can lead to problems like fungal growth and scale rot. It might be worth rationing it to the week or two before its due to shed (the time when they're most likely to need raised humidity).
Well it happened to one of mine, so I'd have to say from personal experience that they don't notice when they're developing scale rot and they don't take the necessary corrective action i.e. staying out of the moist hide. Perhaps it's just one of those situations peculiar to captivity that they haven't yet developed an instinct for?wouldn't it sort of be a mal-adaptive trait for a snake not to recognize it was growing fungus on it and developing scale rot? You would think that like the whole heating/cooling mechanism that lets them know when to adjust body temp, there would be a similar instict to say "too much moisture, need to go dry out" . . . .
Well it happened to one of mine, so I'd have to say from personal experience that they don't notice when they're developing scale rot and they don't take the necessary corrective action i.e. staying out of the moist hide. Perhaps it's just one of those situations peculiar to captivity that they haven't yet developed an instinct for?
I guess it's the same sort of problem that means they can sit on an over-heated surface until they sustain burns, rather than moving off of it as soon as they reach their optimum temperature or begin to experience physical damage.