I have used plastic wrap before, but I like shower curtains better. One large shower curtain from Target costs about 5 bucks and it can wrap around three sides of the enclosure. I only need one shower curtain for an XL zoomed screen cage. The best part about getting a shower curtain is that you can get it in different colors ( I chose solid white--which I suppose really isn't a color...). Additionally, if you choose a nontransparent shower curtain (instead of plastic wrap) your chameleon will feel much safer since she will only have to "guard" herself from one side of the cage as opposed to all 4 sides. I noticed a big difference when I moved from transparent plastic wrap to a nontransparent shower curtain. IMO the solid white shower curtains looks niiiiiiccee.
Also, how many plants do you have in your cage? Plants + Soil tend to keep in the humidity quite well.
I found that doing a rain dance really helps as well.