There was a winter pkg option not sure they still have it.
If you have a tinfoil duct from furnace at mid coach compartment drivers side you could add a 12v fan in duct with a switch mounted were ever you want to install it.
On the furnace control board there must be a 12v control to feed the 12v to fan because mine will cycle when the furnace goes off and on.
Have had this option on all three coachs and it does keep the bays warm just make sure you have all ports for water hose and sewer closed.
Just checked for option and its not listed on Newmar site or Lee's build your own new options for 2008's. But that doesn't say its not possible to still put in. If it stops raining I'll check control board to see if I can find leads for 12v off it that feed the fan.