This really interestes me as well...i changed to mulch and been having 85% percent humidity in my plastic cages (i didn't dry out the mulch before puttiong it inside) but i don't have any wet substrate or condensation so i'm not worrying. dripping is bad because it drops the temperature and makes the substrate a fertile ground for bacteria.

well i have the problem every year when i don't need to heat my house any more. but hey it's the rainy season in africa so maybe it's a good thing.