After I found that the master switch in our trailer did not cut off all draw on the batteries, i installed quick disconnects on the battery clamps - a quick turn of the knob on each battery completely disconnects the batteries.
I do this if I am storing the trailer with the batteries installed for any period of time - although more often, I take the batteries out and take them to my home.
Also, if we are camped anyplace where I will be hooked up to 110 for a long time - say a couple of weeks or more, I open the battery circuit after a couple of days so that the batteries will not be continually subject to charging voltage. I don't know if that is important as I think the charger in our trailer is "somewhat smart" but it is not one of the newer high tech ones that are recommended. I figure it couldn't hurt.
I use AGM batteries that are supposed have minimal self discharge, and they say will hold charge for as long as a year.
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.