I had to add a lamp to decrease my humidity. Right now Ive got a 40 gallon with a 65watt bulb and a UTH. Add coconut husk substrates and you've got a 80% humidity setup. (80% might be too high)

Dont know much about mulch, but I've had my coco husk for a week now and its still damp, haven't sprayed it once.

But I dont think mulch or coco is good for bedding (hide substrates) as it might rot there belly's over a long period of time.