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I've never overwintered dats since they are so easy to grow from seed. If you are determined, I'd treat them like brugmansia that are over wintered. Don't cut them back and keep the soil a bit less than damp and near the light. Cutting them back will cause new growth to start.
About a month before your last frost, give them a shot of half strength liquid fertilizer to break the dormancy and start putting them in an area where they will get a few hours of morning sun each day. When you start to see new growth at the base, you can either cut last years stems back or see if new growth starts on the old stems.
By my experience, my 'make-ship' green house, an unheated basement where the temp. is kept above 60 degrees F. With a little help of a circulating fan (not directed at your plants, but just so to help air circulation), and some inexpensive florescents, or workshop light. That serves the purpose. I overwinter hundreds of tropical plant this way, and some such as my tropical hibiscus goes on blooming during the winter months. I don't see why Dats. won't flourish under this condition. Maybe a little less optimum, but it beats the cold draft days of winter, with no foliages or blooms. :-)
Lily, I have shop lights on the counter and table in the kitchen, plus shop lights mounted over 2 windows for hanging pots, etc, but cannot use the basement. Access is difficult, there is a low ceiling, so basically it is an archive for the winter. I might get down there once every 6 weeks or so. Don't get me wrong, it's a good idea but just doens't work in this circumstance. I had a nice brug that survived one winter there, so there is some hope that the dat's will survive. I think I'll take some cutting and keep upstairs. While the dats are easy to start from seed, by the time my black currant started blooming,it was the end of the summer. That's why I want to keep the plants over winter. If I can get that to work in my circumstances then I can get some more brugs or dats for my collection.