I believe they may be the cold air return for the furnace. There's no ducts connected, but they allow air to where the furnace is located. I've had other rv's with similar openings. As long as you aren't using the furnace I would think you could close them off, but would want them open when the furnace kicks in.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL