I don't cover my plants soil. But I don't really believe in substrate for chameleons. My veiled practically never goes on the floor because he has a million other things to climb on so what would even be the point?
Impaction can be avoided by cup feeding but I'd rather not chance it because I let my feeders loose in that enclosure ^_^
Besides worms which go in the cup.
As for people thinking my enclosures expensive- HAH I spent 100$ for my cage and that was with shipping.
As for drainage- mine doesn't require anything that intense because the foliage catches all except a few drips which are stopped by the paper towels. I have a small piece of visqueen under the enclosure as well. I have yet to purchase a soft tray because I don't really need it but at the same time ill probably buy one just to ditch the visqueen.
Soft trays have a shape and will not collapse but are called soft because they are not made from PVC like a lot of trays are.
Here is an example
http://www.joshsfrogs.com/reptarium-soft-tray-100-gallon-tall-for-sale.html