A seasonal tip for this unseasonable weather, told to me by a nursery man to help avoid frost damage crack the vents open a little on your greenhouse.
Crazy not at all there is science behind it. As air cools it becomes saturated and the water has to condense. To achieve the phase change latent heat has to become real heat and that will slow the temperature drop in the greenhouse. With vents open a little the drier air can escape and be replaced with moist air which repeats the cycle till dawn. Without it the liquid water will become ice and thats what hurts the plants.