A 40 gallon tank is waaaay too big for a baby ball python. How old is your snake? If its around a foot and a half or so it should do good in a 20 gallon with at least two secure hides. A snake in an enclosure too big for it will become stressed and probably not eat. I would definitely get a smaller tank. You could always buy a plastic tub from walmart or some other store and melt some small holes in it for ventilation. The plastic tubs work better to hold in heat and humidity.