You can try dampening the substrate under the aspen but I would get a misting bottle and mist down a lot of the aspen as well. I have two getting ready to shed right now and lately the humidity in the house has been only around 40% so I really try to pay attention to who is in blue or showing pink belly and then spray down their tub with the misting bottle focusing around their hide box, I have used the dampened moss too and put it around the hide box and inside, both with good results. Funny thing is tonight I was performing my nightly spot check for water and cleaning and discovered one of my guys had shed during the night, I had no idea he was in shed, totally missed it on this one. Good news was despite the low humidity he had a perfect shed.