When I owned a diesel pusher with 4 batteries, the front two always required more water than the back two. Also, the charging systems on many RV's do not reduce the charge amount to match the level of charge in a individual battery. The result is the water can get "boiled out" of the battery(s) if the unit is stored plugged into a land/house circuit all/most of the time. My recommendation is to unplug your RV with a fully charged battery, turn the battery disconnect switch to OFF. If you wish, replug it in from time to time if your concerned about the battery becoming slightly discharged while in storage. IMHO this shouldn't be a major concern unless the storage period stretches into many months.
Days camping (2015)----88 days
Days camping (2016) ---110 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi
30 years RV'ing
12 different RV's