I haven't spent any storage time in the deep south, but I have Maxx vent covers for my Fantastic Fans and I leave them open 24/7/365 while in storage. I have done this with my last trailer for a total of 19 years and have never had a mold or cooped up smell issue. I know your humidity is higher, longer down there, but with two vents open, enough air seems to move to be effective.
"If the women don't find you handsome, they should at least find you handy." - Red Green