- I have the same issue, I was perfect temps/ RH % when lights on. Then for lights off it would drop to 50-55 f/ and 20ish %RH.
A member suggested to go to a 24/0 light cycle and I did. No problems with my grow. A debate will start about giving the plants a "rest" or lights off period. But with those autos, as you may know, your time is limited.
- get a very small heater, that does blast a hot stream of air/ or I have seen very effective heating mats you place under your grow tent to keep temps warm( heat rises allowing the grow room to stay heated).