Cover the top, soak cypress mulch before putting in, add moss for sheds. I used a $3 piece of 1/4" MDF from home depot to go over the mesh top, just had to cut a hole for the light.
Your heat bulb might be too strong and is killing your humidity. I was able to lower my wattage and maintain more heat and humidity just by reducing the amount of openings.
It's a balancing act, but once you find it...it's really easy to keep. I'm in maybe every 2nd/3rd day to clean out peeps and poops anyways.
Mine shoots up as high as 70 humidity and drops down to 55 after 3 days. While pretty much staying in the 90-92 degree range.