Mist the enclosure to get it up in humidity. The towel basically only helps in RETAINING humidity. I have this exact same problem. Spray enclosure, cover top with wet towel. 65% humidity all day err day. And I have a heat lamp too. Substrate also plays a huge factor. But for a better solution get a small shoebox (plastic) fill it with water and put it on the hot side. The evaporating water will keep the humidity up too.