I am having some trouble keeping my humidity in the 50%-60% range.

My temps are good (82-84 on the cool side, 92-94 on the warm side, ambient consistently around 80). I use shredded aspen for substrate and my enclosure is a 10 gallon glass tank that has been set-up and insulated with foam board insulation on 3 sides as I read about here. My humidity stays around the 30% mark unless I mist, which I have been doing regularly.

My heat sources are a UTH and a heat bulb, both of which are on thermostats to maintain the above temps.

What can I do to improve my humidity? Would another substrate be better? Any advice is greatly appreciated!