Bill, I am in zone 6 b.
I have tried in the early years to grow them in different spots in my garden and I have always lost them. Then it was pointed out to me that at the Heart's Ease greenhouse ( Orchid grower) in Tewksbury, the Bletillas were growing right against the greenhouse wall where they were very much protected.
So I planted (many years ago) some against my South facing house wall and that seems to be a good spot for them. They only grow in a swath a bit wider than a foot along the wall and hardly spread away from that. To answer your question, yes, they do multiply.
That spot gets full sun and surely the stone wall provides some stored warmth. I mulch them well in Fall by throwing a large pile of leaves over them and remove that when I see the first crocus nearby coming up.