Umbrella plants work well also and provide nice foliage and branches for your cham to use to climb. As stated above an automatic mister helps along with hand misting and using tarp or shower curtain does help a lot. I keep my cage on a metal shelving unit and wrap the back and sides. You can always just mist for longer periods of time or more frequently just Make sure you have proper drainage set up.
I have humidity problem myself. I have a 6 mo Panther in a cabinet/dresser habitat. I cut out the sides top and front to put screen. I have a mist king running 3 times a day or 5 mins each and i have the wife's hello kitty humidifier running for 30mins in between misting. I covered up the screens with shower curtains to try keep humidity in. The highest humidity i can get which is last night with no lights and no heat lamp is 41% i woke up this morning and my hygrometer said the lowest was 20%. I know i can get my humidity higher by running the humidifier 2r/7 but i dont want him to get sick. I even changed the battery on the meter this morning thinking maybe its low. He just went on his hunger strike 4 days ago. BTW i live in California high desert.
My encloser has low humidity as well for the past week due to the wind, even though I have live plants, draped shower curtain on 2 sides, auto mister, and a small humidifier! I'm running out of ideas...
My vet recommended keeping a dripped going constantly to keep the humidity a bit higher. I haven't cleaned my old one up to use it yet but I plan to. I use a mist king right now with five sprays during the day ranging 3-7 minutes and a 15 and 30 second run at night and still find it hard to keep the humidity up with a humidifier. I also have a shower curtain on the sides and back of my screen cage.
Woah lots of humidity issues here, humidity is a big factor in keeping chameleons hydrated, it might be difficult to keep your entire enclosure at 70% humidity so provide a pocket of dense foliage that your chameleon can access with high humidity, I personally wrap my reptibreeze in 3m clear plastic in the winter on 4 sides only leaving the very bottom and top screen open for ventilation, I run a mistking several times a day along with a cool mist humidifier, together they make a fog that helps keep the humidity at a nice level, but I do allow my cage and Cham to dry out several times a day, it helps keep mold and respiratory issues at bay. I make sure I hand water my chams and watch them drink from a spray bottle to make sure they stay hydrated. Humidity is definitely one of the biggest hurdles when it comes to keeping chams.good luck! Btw keep that humidifier clean.
Make sure you guys use a good hygrometer, use one with probes, you can set up your probes in the pockets of your cage, keeping the gauge up high will throw off your readings since the lights keep that area dry!