Is yours installed in a cubby hole like ours? Never heard of freezing temps damaging them. I can understand if they still had vacuum tubes that need to warm up though. The only thing I can think of is that if you turn it on during freezing temps it could build condensation.
It may be true, I don't know. However, there is one thing I know and that is that you cant trust a salesman. They'll tell you anything that they've heard even though they haven't verified it themselves. Including that a 351DS gets 14mpgs. LOL