Worm BIN temperatures can be kept much higher than outside temperatures by feeding food scraps (which heat when they decompose as you know) and by using heating coils or simply insulating your bin.
Also, buying a compost thermometer will help you monitor the temps.
I personally feel heat is far more dangerous than cold. Worms tend to go into a hybernation type state then rebound when warmer temps occur but in the heat they MELT.

Where we live it is hot in the summer and very cold in the winter. All of our outdoor worm bins are large and open at the bottom to the ground so that the worms can go into the ground if conditions in the bin don't suit them. We use recycled olive barrels with the bottoms cut off and lots of holes drilled in the sides. They are located in a sheltered spot that gets shade in the summer. We started with 2 pounds of worms in 1979 and still have thousands of their offspring so it has worked very well.

It can get up to 99 here and then as low as 9 some winters. We were told at the vermiculture class that we shouldn't let the worms go into the ground. I forgot why. Invasive? Kill the other worms? Sorry I don't remember. We also have armadillos that love to eat worms.

I have no experience with cold weather wormin', but I do have large wormbeds right on the ground. They are covered with old carpet from a recent remodel, which keeps a wide variety of critters outof my squirm. Check out redwormcomposting.com for info about cold weather wormin' by Mark from Kansas. He keeps them going by "winterizing" his beds with tarps and straw.

Good luck, Pete

I used to find tons of red wigglers under leaves that I had piled over garden beds when I lived in a place that had winter lows of 25 or 30 below zero. I don't know how they did it, some form of hibernation I suppose, and they were under leaves and snow and not exposed directly to the air temps, but they were fine.

In my current climate, we have lows in the teens, sometimes low teens and my bin is fine in my unheated garage. They aren't nearly as active, so be careful not to overfeed, but I think your bin would do ok outdoors though I'd suggest giving them some protection if you can.