most people do bare just encase your cham ingested it and causes it problems which could potentially (if bad enough) kill them. Plus bare makes it easier to clean, right now I have paper towels down to absorb the water falling since I do not have live plants to do that for me
I use moss to cover the soil of plants I did not grow myself. The little pieces of perlite are much more dangerous to injest than moss. But for the floor you'll want to keep it bare. For the sake of cleaning I mean. Substrate in general is a big no no. Get some frogs if you want a really trippy naturalist terrarium. It's not good for chams to be put through that.
Like other have said bare is best I use a outdoor carpet that is made of natural fibres and resists mood for looks in the bottom of my display setups. I get it at Home Depot and it's a nice dark green color with a little pattern in it. Not the AstroTurf stuff lol