Difficult to say.
I have a minimum -maximum thermometer in my mini greenhouses, which are still inside my big greenhouse which is otherwise unheated. In there, they have been staying at 10 degrees, occasionally as low as 5 but I then use fleece over the plants as well. You should get a few degrees warmer, but watch out for overheating past mid morning, mine are reaching 25 degrees if I'm not quick enough to unzip the plastic covers!