Ventilation holes. A drop of silicone to a magnet affixed to the front right above the clear door. Another magnet glued to just about anything approx 1 inch high keeps the door from opening from the inside or outside until the magnets are pulled apart. The top is very secure. I got some heavy duty Velcro strips to attach a tap light to the inside of the lid.
The one in the pic is for a baby boa. I've used another for a leopard gecko. I stick my heat mats to ceramic tile and put the boxes on top of it.