When your ambient temps drop like that and you've got all the right stuff for the cage, chances are its not the cage setup...it's the room that the cage is in. These questions show up every year around this time when people's houses are colder than during the summer.

Say if you have a 50w bulb/heat pad giving you a 92 degree basking spot in a room that is 72 degrees, you will not still get a 92 degree basking spot if the room drops down to 68. If you are using a thermostat, your basking spot may remain at 92, but theres no way that the heat pad will be able to continue to support the higher ambient temps you need.

So, fix the room temp and your cage with follow suit. Space heaters are a must have for any herper living in a climate with cold winters.