There are several charge controllers that will be damaged if the battery is disconnected with live PV still connected. I don't remember which models but I have run across them over the years. Whatever charge controller you get you will need to read the instructions to see if this is the case.
I would put the controller with the batteries. Are the batteries on all 3 trailers the same or are they different sizes, types, brands, etc.?
You may need to program the charge controller differently for each battery bank to get optimum charging. Yes, generic settings will work well enough but specific settings will be better.