Just found this thread...I have a Mandevilla on the South wall of my greenhouse for about three years now, it never gets below 50 in there and it overwinters quite well. I'm in Zone 6. It has a few red blooms on it right now.
Bought a Dipladenia this year and brought that in as well, it's not blooming but is growing up a wire nearby that I have to keep nipping off.

Mine twined around the cords of the Venetian blinds. The new blinds are cordless but the plants are history.