You can try 2 different things:
1) Get live plants if you don't have any in there, this helps the humidity stay up between mistings. I have tested this and can confirm it helps. I have a Fig Tree in my enclosure for my Chameleon, it's in a pot on the floor of the enclosure and it reaches the top of the cage pretty much. If you decide to get live plants, make sure you get some that are not toxic to your Chameleon. Here's a
list. Make sure to switch soil of any live plants to soil without any pesticides or chemicals.
2) Other people on here use shower curtains (cut and tape to enclosure or how ever you want to attach) to wrap 3 sides of the enclosure and this will help keep a lot more moisture in as well. I have not tried this as the live plants worked well for me.