I keep them about 15 per take-away container with the lid pierced every inch or so, in damp sphagnum moss gleaned from the lawn, They are fridged in my bait fridge and checked for condition every week and the sphagnum moisture checked. It should be wet but there should be no loose water in the container bottom. Soil fouls the moss and should be avoided; even a small amount.
They go completely torpid like this without freezing or going soft and will liven up within a 1/2 hour when removed. If you only put whole worms in there they will not decay and I've kept them for up to 3-4 months and then buried them in a composty corner of my veg patch to recover completely.
I usually take new stock off the lawn at night but if stuck can always dig around Compost Corner. I can't remember when I last had no worms at all.
I also keep Dendrobaena (Tiger Worms) like this but they start to go a bit flaccid (soft and spongy) if they don't get a feed after about a month, so I put them back in the composter and rotate them with new stock. I keep about 30-40 Tigers to a container.