full water jugs place them under the lights among the plants so when the lights are on they collect heat to be release during dark time, the soil is what you need to keep above 55 60 degrees the tops can take near freezing but 40 would be as low to go. they make rigid 4x8 insulation foam panels you can get em at a building supply store you could make a box that you could put the plants in at night or a box for the whole grow........good luck