Warmer air holds more water vapour than cooler. Glass does NOT absorb water nor does glazed ceramic like a CHE. Humid air rises, CHEs and bulbs are usually vented with screen and allow humidity to rise they tend to also increase ventilation. The question isn't how to lower the RH in the tub but what is the RH in the room? You will not easily be able to drop the RH lower than the rooms RH. 70% is not a problem if coupled with good ventilation. My rule of thumb is with dry substrate and no water bowl the RH should be the same as the room in one hour or less. (one air change per hour).

Smell is a huge over looked sense. If it smells anything other than fresh you need more ventilation and a good cleaning.

lowering RH in the tub (if it is much more than the room) more ventilation remember warm air rises and cool falls, High and low holes will increase air flow much faster than just top. Substrate choice and water bowl size and location also have a huge impact on RH.