It's perfectly fine to use a substrate in a glass cage, and it will not stay very wet if you have lots of plants in there sucking up moisture (you will just have to figure out the spraying schedule to get the proper balance). Try the ABG soil mix, or just peat moss, or coconut fiber and cover the top with magnolia leaves, oak leaves, and/or catappa (indian almond) leaves. This creates a barrier between your chameleon's tongue and the substrate. It's much more dangerous to have sitting water (yes even on paper towels) in there which will lead to bacterial infections. Just make sure that when you are mixing the ABG mix, to take out any choking hazards, and maybe use very large pieces of bark (which helps with aeration). It will be difficult to do BillB's suggestion because you will have to remove those vines and branches every time you clean (which would be daily if you are only using paper towel), and this may be a deathtrap also if he gets stuck underneath or his tongue gets
Bonus tip: buy a colony of tropical isopods and tropical springtails online, this will breakdown poop, shed skin, debris etc etc.
Here's my big exo terra setup for a jacksonii.
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