Maybe a check with a multimeter would put your mind at ease. About the only thing that will boil out battery fluids is having 13.6VDC or more coming from the converter/charger unit for a long period of time.
Your smart mode PD4600 series converter should drop your battery voltage down to 13.2VDC when nothing is going on. It will jump between 13.2VDC and 13.6VDC when being used.
When it needs to re-charge it will jump up to 14.4VDC for about two hours and then drop back to the 13.6VDC level.
I suspect some condensation is forming on your batteries since you have NOT noticed the battery levels dropping.
Something to watch however...
I originally had two GP24 standard issue 85AH Interstate batteries when I first got my Trailer. It was equipped with an older single mode ELIXIR charger and it wasn't no time before I boiled out one of the batteries making it unusable.
I then added two more standard issue 85AH Interstate batteries and replaced the converter/charger unit to a PD9260C and all has been well now for the past 5 years or so. I still check my fluid levels on a regular basis out of habit but always find them ok.
Roy Ken