If you don't use the hydroball drainage layer, the soil will get waterlogged and possibly smelly because there will be a fair amount of water due to the misting and (hopefully you have one) shallow water area for them. The hydroball set-up is really not difficult. Most hydroponics stores have hydroballs. Just dump them into the enclosure to a 2-3" depth. Get some vinyl screening from Home Depot or equivalent, cut to fit and put it on top of the balls. Then use coco fiber (you can get it in compressed brick form) for several inches on top of that. If you change your mind and want to go with live plants, pothos and sansevieria work great. I also put a big piece of wood in there to kind of hold everything together.

Aliza