Camping with two puppies in December

I would be very careful and not overdo it. If your puppies have been exclusively indoors, their fur differs from an outside dog. Outside dogs have greasier fur to protect against moisture and they get used to the lower temperatures gradually.

You should at least put up a small tent for all three of you to bunch together at night for warmth. That also strengthens the bond between you. Put an insulating mat or thick blanket on the ground, so your dogs don't sleep on the cold floor.

Take one or two old towels with you if you expect your dogs to get soaking wet. Make sure their lower back and abdomen are as dry as possible when you rest. If a dog arches their back and makes a hump, return home and see a vet to exclude an infection of the kidneys or bladder.

Both German Shepherds an Border Collies have long enough fur to survive in such temperatures, but if your dogs are shivering, consider retreating into the tend for an hour or two to warm up. Dog coats (as stupid as they might look) are a good way to keep your dog warm and dry, but are no must have for these breeds. In the worst case, cut your trip short.

From experience of growing up in certain region, outdoor German Shepherds of my neighbors started to freeze to death around -30C, so -3C is nothing.

Not sure how far is their thermoregulation at age of 5 months, though.

I would however bring the tent, just in case (wind-chill/freezing rain). Also couple towels to dry those happy pups.

I reckon you could bring them with you under the tarp, I suspect they wouldn't mind?