I make my holes with a sottering iron. For boas and pythons I put one row of holes towards the top all the way around the tub and I space the holes about 1 1/4 inches apart. This seems to be enough holes to hold in heat and humidty and allow air to circulate. In my setup I can move the water closer to the heat to raise humidity and further from the heat to lower it. I don't count the holes I just space them evenly. Since a picture is worth a thousand words, here ya go...
Good Luck