Just another place or thing to check is your windows and vents. If you by chance have a window open, the exhaust can come from the rear to the front and into the open window. I forget what the term is but the air can travel between the sidewall and the air coming off the front of the coach. Every once in a while my co-pilot will open the window in the toilet room and the coach will fill with diesel stink. I pull over and check the windows and will find a window slid open or sometimes the over head air vent will be open, without the fan being on and the smell comes in there.
Good Luck
Happy Trails