Is it possible that you have, or have had, a water leak somewhere? Is that smell musty? I would check all areas that are susceptible to water intrusion. (Roof, slides, windows, etc).
Since you are in Louisana and always have high humidity, try a hanging package of DampRid. That always took the stale, damp, odor out of the cabin of my boat.
Another cure might be to install a dehumidifier in your RV. A lot of us use them at different times of the year. Mine is a smaller sized unit that I purchased at Lowe's.
Good luck resolving your problem and keep us updated on your success.
2001 Ford F-350 Super Duty CC Dually, 7.3 Diesel
2013 832IKBS Flagstaff Classic Ultra Lite, Hensley Arrow Hitch, Carlisle tires
2016 days camped....211, it ain't over yet!
On the road to ALASKA May 6, home Sept. 13, 2016. 23 states, 3 Canadian Provinces, up to the Arctic Circle, 17,300 miles, 131 days on the road. 1 flat tire, 4 oil changes. What a beautiful trip!