Personally I don't like reducing ventilation for the sake of humidity. I also would suggest that hot only is paper towel a poor choice for humidity (hygroscopic) it is also one of the most potentially dangerous accidental ingestion of paper towel is often fatal. I would suggest something else. Personally I would look at coco coir (eco earth) it holds more water than any other.

The method I employed with an open top system was to bury a plant tray under the substrate on the cool side (very thick layer on cool and thin on warm) the tray can be filled with water just by poking a finger down to it and adding some water. This water mass humidifies the enclosure.

Personally I target 50-60% with upper 50s-60% for a shed there is no need to have higher than 60% (accurate) as most bp shed fine at 60%.