I had a huge problem with humidity in my tank too...due to stupid electrical heat in my apartment :S. With suggestions from the great people on this site I have found out what works for me. So here it goes....
I placed a few layers of of tin foil covering the top of the cage, keeping an opening for my heat lamp.
I also have to spray the cage every morning and every night.
I also use repti bark with this coconut stuff (can't remember the 'real' name of it), but I find the mixture really helps with moisture... especially when i spray it down it helps to keep the humidity up.

These are just suggestions that other people have given me...and they work for my situation....

Hope you find something that helps