If the tank is properly set up, with the under tank heater plugged into a thermostat to control the hot side temperature, you shouldn't need to do that. You need a thermostat to control the under tank heater otherwise it can and will burn your snake. You then need a digital probed thermometer and hygrometer to monitor the surface temp of the hot side where the under tank heater is, and the cool side (ambient air temp), and to monitor the humidity.

If the required hot side, cool side, and humidity can not be maintained in the tank with an open screen lid then cover most of the lid with foil. Leave just about an once or so on one end for ventilation to start until you know how much you need covered.

If this still doesn't work, you may need to supplement with a low wattage heat lamp but still keep the rest of the screen covered where the lamp is not at.

Please look at the care sheet on here for more info.