i know that jax need higher humidity than veield and panthers so I cannot be specific, but I can tell you what has worked for me. I have a shower curtain liner on the back and sides of the cage - cheap, easy and attached with small cable ties. I then use a humidifier/pvc pipe setup on a timer for added humidity. I live in NH and the winter is bryutally dry. In the summer I would use the a/c on very hot/humid days (critters are in my home office and I cannot bear the heat) but even with the a/c I did not have near the issue as in winter.
Lots of live plants will help increase and maintain humidity - stuff them in there and mist thoroughly.
Hvae an outdoor cage for sunning in summer and hose it down (with cham inside).
Winter, a weekly shower will help, too.
Do you live in the north?
See these two articles on chamnews.
and I included some pics of my setup.
http://www.chameleonnews.com/humidifier.html



Up North Caging
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Chameleon Help & Resource Info
1.0 Nosy Be Panther Chameleon - Cyrus
0.1 Veiled Chameleon - Luna. She's now hanging from her big jungle gym in the sky
1.0 Beardie - Darwin
1.1 Side-blotched lizards - swifty and blotcha for now 
0.2 felines - Kyndra and Lita
0.1 African Clawed Frog - Skipper
0.1 Mad. Hissers and she's back!
0.1 Chilean Rose Hair Tarantula - Rosa Leigh Died 4/21/06 
0.1 Goliath Bird-Eater Tarantula - Natasha donated to science 4/4/06
?.? Pinktoe Tarantula - no name yet