I think, in a "normal" year here in Maine (what ever that is) that the conditions that contribute to chalkbrood are short-lived but our springs can be cold and wet, and that can be a factor. Perhaps some insulated boxes would be helpful at times.
I was wondering last night if I was a bit premature in hiving that weak nuc yesterday, but it just looked so much more healthy with lots of capped and uncapped brood and honey stores than when I put it in the 4 frame nuc, they had no room to expand at all! In 4-5 days they'd be boiling out of there- I figured it was time.
Michael Bush told me I'd be "pleasantly surprised" at how well they did in a small NUC. He was right.