A copper Classic Moulder Strip (CMS) is good down to at least -20F without a cozy. A slightly lighter weight of aluminum would be good to the same temp.
I haven’t tested side-by-side them yet (haven’t had any days off when it’s below -15F) but I suspect that two layers of aluminum flashing would go to at least -10F.
Realize that the heat transfer would be additive. Make a 2-layer aluminum T. Make a 4- or 6-layer aluminum T. Bring them both. They’ll only be like 10 or 15 grams each. Try the lighter one. If it isn’t keeping up, try the heavier one. If needed, use both at once. And/or use a bandana as a cozy over the Moulder Strips.
One advantage of folding the flashing for more layers/thickness is that you get mostly folded edges instead of cut edges.
Rather than a file, I use a belt stander (not hand-held, but on a stand). Or hand-sand the edges with fine sandpaper or a Scotch-Brite kitchen scouring pad. Wear leather gloves until it is smooth.
Not for up in the flame, but at the base, clear fingernail polish can be applied to the cut edge. It also can protect dings in your car paint from rusting, sometimes improves visibility through a chipped windshield, and can bind a torn fingernail back together so it doesn’t tear further.