It is slow, yes. But I am encouraged to see the group is still getting some activity.

Living in California, I don't have much advice for you about "wintering" trees unfortunately. I will say that Satsukis are very different from Junipers, and I find them to be more temperamental. You can winter trees in a garage with a window, or in your yard covered with poly material, similar to what they use on greenhouses. A greenhouse that doesn't get too warm would probably very nice, but you don't want it to get too warm or you might interfere with the plant's normal phases.

I will say from my experience that soil and drainage are very important for Satsukis, and you don't want too much sun in the summer. My first Satsuki died during a rare wet winter in CA due to root rot. I repotted that spring in pure Kanuma soil which is its preferred soil but it was too late I had already lost more than half the roots.