You can remove as much dirt as possible, and then store them in moist, not wet peat, so they don't dry out. Brugmansia are very heavy feeders that should be fertilized every watering.

Thanks @Jay 6a Chicago for the reply. For sure I wasnt clear in my original post ie my intention was to keep them very much dormant in a cold cellar until next spring and I would imagine like many other plants that go dormant they need basically no water.

Although they're not going be actively growing you don't want them to dessicate. So they need keeping slightly moist. That involves monitoring and very occasional light watering.

Again I left out key info in that this morning I potted up both in potting soil, as I often do with dahlia tubers; and with dahlias I actually never water them during the winter when they are dormant and under soil.

I read an article that said they should be fertilized 2 to 3 times a week, and another article said to water once every week or 2, but I know people have great results with fertilizing at half strength at every watering.

Dahlias have fleshy tubers which store moisture. Brugmansias don't so they should not be allowed to dry out completely. Indeed, even Dahlias won't survive if they're allowed to get dehydrated.

The feeding advice, of course, is only for the summer when they're actively growing.

They are absolute pigs. The hungriest plants I know of.

Good point @floral_uk z.8/9 SW UK ie the tubers are able to store (some) moisture.

even Dahlias won't survive if they're allowed to get dehydrated.

Well ignorance is bliss as my potted dahlias, as stored dormant tubers, never get added water from mid October until February...in fact no water until I see a sign of growth (after being brought up and into the warmth and light). (I guess there must be enough moisture in soil through the whole time it is dormant?)