It is very important that you keep his humidity at around 50-60% and get his warm spot to 93.

Does he have an undertank heater? That with a thermostat is the best way to regulate temps. Increasing temps and humidity are very important to help imune system. How low did temps go?

Check for mucos or fluid in his mouth. If he has an RI you need to get him to the vet. If allowed to get worse he could very possibly drown on his own mucos. Coughing is not a good sign.