In Fl you will probably need to recharge the batteries more than once a month even if you have nothing connected to them.
Jato's experience in northern MI is not going to be what you experience. That is because the battery self discharge rate (the rate at which it loses charge with nothing connected to it) is higher the warmer it is. The rule of thumb is the rate doubles for every 10 degrees C (18 F), so your battery self discharge rate is likely 10 times or more what Jato's is. And you do not want to leave the batteries partially discharged or the plates will be damaged and they will permanently lose capacity.
In your case, with no grid power at your storage site, I concur with the suggestion of adding a small solar charger mounted on the trailer permanently. If you are using dual golf cart batteries you can get a 10 watt or so solar module and connect it directly to the battery through a 5A fuse (to protect the wire from shorts) and not have to have a charge controller. To start with, check the battery water level and add distilled water as needed every two weeks until you get a good idea about how often you need to add water.