I totally agree with InknSteel, Provent-A-Mite is amazing, just be sure to follow the directions exactly. ( Dont spray the snake, dont spray the water bowl, let the spray dry 100% before putting the snake back into the enclosure, etc.)

I use cypress mulch instead of aspen, cypress mulch holds humidity better and is resistant to mold, if aspen becomes too wet or soaked it is possible it can become moldy.