Thanks for the link, DSD! Maybe I can finally find my Rocky Mountain Juniper...Not sure about this as concrete has a low R value. Likely need to add insulating material on the outside walls to keep the air temperature up during really cold spells. Of course, the best bet would be to create a below surface cold frame, similar to your other set up.
Looking for ponderosa, Andy Smith is a good bet.
cheers
DSD sends