Try buying some 12" x 12" mexican/saltillo tiles at a store like Home Depot or Lowes. Be sure to get them unfinished. Soak them in water for an hour or two to absorb the water then place them in the cage. The water evaporates slowly from the clay tiles and should provide the humidity you are looking for. I did this when I had blood pythons and it worked like a charm. You will probably have to experiment a little bit with how long to soak them and how many to use, but once you get it dialed in, it's just a matter of pouring a little more water on them every couple of days to keep the humidity within an acceptable range.
Good luck!
Billy
>>i just finished a plywood cage for my boa, its 4ft long 3ft high 2ftwide. the humidity was only 30%,i was told on this forum to put a household humidifier in the cage and even with that as soon as its turned off the humidity drops back down from 60 to 30. im starting to think im gona have to cut a foot off the height even tho i already finishd the cage. is ther anything i can do??