I think I would prefer an unheated garage as heat can accelerate rusting I believe. I may be wrong on this, so maybe someone can clarify.
Mine will be 3 months in an unheated, but insulated, garage and on the battery trickle charger.
2012 328iTouring xDrive Black Sapphire
Waiting for: 2016 340i xDrive MPerf. EBII
Previous BMWs - 17 others since 1971.