Yep. I had one that was 8 x 8, and covered with plastic drop cloth. A 100 watt light bulb will keep it above freezing. The plants will go dormant until it warms enough for them to continue growing.
I have some pvc pipe that I criss cross by putting each end of 2 pipes in the corners of the 3x8 beds. This keeps any plastic about 18 to 24 inches above the ground. I can hang the light from the center where they cross.
We always have rolls of plastic covering around for Hubby’s concrete flatwork.