I use a tub as well almost the exact same setup you have, and started off with aspen chips as well. Thing is, the tub holds humidity almost TOO well. I switched to paper towels and my humidity balanced out at about 63% now. It's really just up to you, you can use paper towels instead of aspen, or use aspen and drill more holes. Simply because aspen itself holds humidity very well too. So aspen+tub= super high humidity. Lol