Maintaining RV batteries

RVs should come with a decent maintenance charger but they don't at least most don't. I believe they overcharge. On ours, if not plugged in, the RV slowly drains the coach batteries running the gas sensor. To stop this I installed an isolator solenoid with a remote switch and voltage meter right at the doorway. It's fine for a month or more if it's isolated. I'll plug it in for a day or two once a month or so. I also installed a trickle charger for the engine start battery that plugs in to the coach system so it gets a brief charge on those days.
Previous posts did not point out the part about the isolator preventing drain.