a 20 high would always be better but if you have the long just have a lot of vines/sticks going diagonally from bottom to top for them to climb on. I use reptile carpet, unless your planting thats what I recommend. The soil/bed a beast stuff is a mess, just find a way to keep your humidity up. With a 20 long you can cover half of the screen top with saran wrap, and spray all the sides and with the heat you provide you should be able to keep it up without a substrate, i do.