I have kept my ball python in open screen tops for the whole 7-8 years I have had him...at no point have I covered this screen with a damp towel...that's called asking for mildew, at least here in the south east. Like many have said, a more efficient substrate will likely alleviate the issue, I use coconut bark for my BP and I saturate it very well on a weekly basis...he has never experienced a bad shed. The only catch with eco earth is I have found it to mold rather easily, but this is a simply fix: add a light top layer of cypress mulch, it has a natural acidity to it and will inhibit mold growth.