Cold Air Return for Furnace??

[dersequim]

I remember there was a thread about being able to see light from Basement, under sliding door! Well today I was talking to my friend who has a King of the Road and he mentioned that his KOTR has a grill on the interior wall of basement. So he called Dealer to find out why? He was told they have that there so the Furnace can pull air just like the Cold Air Return in his house.
So did WE ALL plug up our CAR? Also he was told NOT to leave anything down there that could emmit fumes!! Any COMMENT Montana Answers?? lol

2004 2955RL
1997 RAM 2500 Diesel, Auto, 2WD, LB TST #8 Fuel Plate, Pac-brake, BD Auto-Loc, BD Pressure-Loc, Ranchos, Firestone Ride-Rites, Diamond Plate/Toolbox-Bedrails-Running Boards, Vent Shades and Wind Deflectors and Fender Eyebrows.