We do not leave our RV in Florida over the summer months, but several others at our park in Crystal River do. In nearly every case here they leave their units plugged into electric and set up a dehumidifier that runs into their sink or shower stall. One fellow in the park lives here year around and folks pay him $15/month to check on their units twice a month to make sure all is well within.
One couple didn't do the above and just left it onsite with predictable results----mold. Cost them $1,500 to have their unit professionally cleaned before they could move back into it the next winter.