I put fleece over everything in the greenhouse at night.. except the mini greenhouse.
Reason : one year we had an incredibly cold March night - the temperature was -10C and despite my paraffin heater some of the plants inside the greenhouse were partially frosted. (they did survive).

IAs I said I switch the heater off in the day: we have had snow showers and sun today: the greenhouse reached 20C unheated (it is bubblewrapped as well.)