I too live and camp in Northern Florida and have a Denali 5th wheel. We only have the one ducted unit and it works fine. Make sure the filter is clean as they get full rather quickly. The only time we ever had issue was June 2012 at Ft. Benning and the outside temp was 103. The unit struggled during the day, but cooled off at night. Other than that it has been fine.
2011 Dutchmen Denali 262RLX
2006 GMC Sierra 2500 Diesel