The norm is not to try to winter nucs, they are to small and don't usually make it.
There is a bee keeper in Vermont with some notoriety who would probably disagree with that. I believe Michael Palmer winters 300+ nucs every winter and he doesn’t even use foam hives! He uses thin wood hives.
You would have to search BeeSource for the details. I believe he’s in Northern Vermont, near the Canadian border. He’s probably considerably colder than Finski; there aren’t any warm ocean currents to keep northern Vermont warm. Some pretty good skiing up there too!
Palmer can make the arguments for wintering nucs better than I can. It’s part of his idea for a sustainable apiary. As Finski likes to point out, we have high losses of bees in the USA. Be it mites, cold, wood hives, CCD, stubbornness, honeyballs ;), or whatever, we manage to kill a lot of bees every year. Without a means to replace those losses, bee keeping can become very expensive and un-sustainable for many beeks here.
If you maintain some nucs of your own, it is a way to boost weak hives in the spring, start new hives, or sell surplus nucs to other local beeks.
Edward, I agree with your guidelines for wintering said nucs: Insulate them well and make sure they're packed with bees. When I achieve that, the nucs usually all survive.