That humidity will not hurt him at all, Youll expect perfect sheds all the time every time, And you wont need any messy substrate you can use plain ol paper towel!
The only caution you need to take with that humidity is that the air temp never drops to cold as that can cause concern for R.I just keep a nice 78+/- cool side and 90+/- and hell be a golden happy boy
Times where they live the humidity jumps up to 90+% so hell be 100% happy!
Secondly at 200g you guys prolly only a few months old unless under fed! most yearlings can get 500-600+ as a male!
As for feeding try to get him onto rats earlier then later (if he keeps declining meals give him the mice till hes more comfortable) but itll save alot of effort when hes 500+ grams and needs 3+mice, vs 1 small rat.
Aswell if he does decline again (offer in 5-7days) make sure the room is dark and just leave the rat on the warm side of the tank, most of the time you'll wake up to a missing rat! Which is what my lav spider girl always does! its annoying but she does eat)