i use the towel in a bucket and i am constantly at 45-55 humidity. make sure the bucket has a good amount of water and dip half the towel in the water in my opinion and then pull it out and let it rest against one of the poles on the side and keep about 25% of the towel in the water. have a fan aimed at it like they said above
you can also use a spray bottle and constantly go inside and spray water onto the walls of the tent. but be careful cause it will quickly spike the humidity. i tried it once and went from 35 to 70 really fast and had to air it out to get it back down