You can always cover the back and one or two sides with a shower curtain or something similar to help with humidity. That's how my cage is during the winter months. I don't use reptibreeze, but it's the same type cage.
I use a cool most humidifier, you can create a humidity pocket by facing the humidifier on a section of the cage, allowing your Cham to be able to choose from cool humid area and a dryer warmer section