Instead of making a terrarium-which are more suitable for frogs, try using a very moisture loving bedding like long fiber spahagnum moss (also called orchid moss) and setting up a drop or mister system within the tank to add moisture on 2-3 times basis. Your landscaping friend should be able to help you. You need to buy a few items, have a large reservior of water that will need to refill every few days. They even sell whole misting set ups for frogs in some pet stores or online. They can also be used.
A friend of mine made something from a fish tank pump-added a bubble stone-stuck it into to a large bowl of water that was then placed into the tank. The turtle even began to sit in the bowl and had took a "bubble" bath 
The charcoal base won't work unless the tank is very deep and there is plenty of bedding above it since box turtles like to dig into their substrate. They would soon be living in the charcoal. Good luck! Please use a large tank for these turtles so they will have lots of room to roam and thermoregulate. Tess
>>I'm trying to establish a more efficient home for my baby eastern box turtles that were stranded by their owner at a pet store around a month ago. To keep the humidity levels up in their tank because our air up here in the mountains is fairly thin and our house heat is rather dry so moisture evaporates fast in my tanks (I have hermit crabs too that need 70% humidity), I thought of using live safe plants as well as soil and moss. My mother's boyfriend loves landscaping and informed me that keeping a tank moist at that humidity level with live plants is hard to keep up on because it may mold rather fast as well as other complications. I'm not sure if that is true or not or if anybody has any suggestions. He also mentioned something about using a charcoal base with rocks or something underneath the soil substrate so the substrate does not become too wet over time and mold. I'm really hesitant of this because I am not very knowledgable in this field. Any info. would be greatly appreciated.
