It would probably work in 7B, with a similar winterizing like this one.
This setup has withstood temps in the teens, with zero casualties.
Right before it's expected to go below the plants' tolerance, I wrap with insulation, duct taped together. Then a car cover. And then with tarp for a 3rd layer of protection. Then tighten all that with a rope in a tight knot.
And I separate the insulation that's around the sides, from the insulation on top, since the door opening is on top. And cut the insulation to the
size & shape of the door. That way during times in the winter when it gets warm enough to tend to them, all 3 layers are easily removable, then wrap again when temps are expected to dip again.
The insulation I personally use, comes from those big boxes of frozen dinners shipped by Metabolic Meals.
They're just as good, at keeping cold OUT of my mini-greenhouse, as it is keeping cold IN the boxes of frozen meals for preservation.
That thing that looks like a fan is a screen used for ventilation, after I cut a proper hole in the clear vinyl.
And it has excellent micron level, to keep insects out. It also acts as a "poor man's humidity control" ; If I sense the plants need more humidity, I block it (except winter when it's already blocked).
And I have a flat square full-spectrum growing lamp that fits nicely on the door on top.
This is what my 1st layer insulation looks like and below that pic is a 'splash guard saucepan screen' that I used for ventilation/humidity control/insects etc.
Of course it doesn't need to be done exactly like this, but similar. You can also use burlap, frost cloth, or a heavy blanket for example...
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