Running furnace with slideouts in.

Badger, we only bought the trailer (Hideout 25RKS) last fall. Used it till Oct then put it to bed. It doesn't have a "winter" pkg, but it's called a "Cold Mountain" pkg - I think it's for using in the early/late camping season. I can't remember if it was the dealer or I read somewhere that the tanks were heated by the furnace and could be used, for example, when heading south for a day or two until you get to warmer climes. I've never used it in those conditions so have no idea if it works well. I'm hoping to hear something about it on this thread. I'm also wondering what problems could be created by covering one vent. I'm thinking as long as a couple are free to let the air flow there shouldn't be any issues. But then I don't know very much about travel trailers, this being the first one we've ever owned.