Love chameleons! one way to fill up some of that space is to get a live vine-type plant (Make sure its one not toxic to chams of course). They work great in their enclosures because the UVB lights that chams need will make the plant flourish and you don't have to water it if you run your drip system above it. I would also recommend covering the soil to keep it from being consumed or dug in. I used those decorative flattened marbles that you can find at any craft store