When I went out early afternoon and checked the thermometer it said the temp had been holding nicely at 20degrees over air temp. So barring anything drastic the broccoli should be fine. Cross your fingers!
That’s a double layer of fabric frost protection cloth, with a layer of plastic sheeting over that (I don’t remember what mils, it was what we had around the house), and a single strand of non-LED C9 christmas lights string on hooks on the underside of the A-frame supports (1×6 pressure treated boards left over from building the front steps, the boards aren’t IN the tire-beds, but braced outside it, so the chemicals from the boards shouldn’t be a problem). Once this weather is past I’ll pull off the plastic and unplug the lights, but leave the frames and cloth in place. That way if the weather swings again all I have to do is plug back in the lights and re-drape the plastic.