I have some friends that travel quite extensively, more so than me, and they search out and talk to folks that specifically double tow in FL (some are residents others are not) and nobody has been stopped. The non residents some from Canada and some from Indiana have been doing it for several years. Actually one fellow from Indiana just made his 3rd trip and has passed FHP, GaHP and locals and was never given a second look. There have been indepth discussions with 2 FL residents. One is over the 65 ft length and again no problems. Then another fellow has gone from Ft. Meyers to Stone Mountain in GA as well as towing back and forth to DISNEY, never stopped. He actually told me the catch is in FL it says no to double "trailers" ball hitch and a FW is not considered a trailer per the definition. The consensus - as told by FHP that if your driving "sanely" they have no reason to pull you over. Keep your head about you.
With the above said, this is only a 'drive by' survey so travel at your own risk. However, personally, I also tow a small trailer behind my FW that has my golf cart and I have been quite a few places myself and have never had law enforcement issues in the states I have passed through.