Humidity is best acquired by using aspen bedding and spraying every night or so. I use a $10 accurite digital thermometer/hygrometer combo to measure the humidity. Works perfectly.
Digital thermometers with probes also work well to put under the substrate for accurate tempertures.
Using a under tank heater is the best type of heating method and works the best for a proper gradient. Get a thermostat or rheostat to hook up to the UTH. If the different ratsnakes all need the same heat on the warm side, you can hook up multiple UTH's of the same type to the thermostat instead of buying a new one each time. That way you can buy a 60 dollar reliable thermostat without having to worry about anything.