I had gotten two of the reptile basic hides and at first, they were fine, but after feeding my snake, she would plump up a little and not fit through the opening. From what I understand the size of the opening doesn't change throughout the bigger sizes. They are however light and easy to clean and don't take up that much space as they aren't super tall, that being said my little girl loves coiling into a taller coil rather than a flat one and so she pushes it up more. I now have two Exo Terra reptile caves in a size large for my 3ft BP and she really loves them. They're a bit more frustrating to clean and are a bit heavier but she tends to like them a lot better, and they fit nicely into the 40gallon tank. Just my input on hide boxes.