My $.02 is that there's a difference between "a full timer plugged in" and "plugged in for storage." Specifically, when the RV is in use, various loads are drawing the batteries down while they are also being charged. This reduces the chance of overcharging and boiling the electrolyte out.
I do not know when (year wise) Converter/Chargers became at least somewhat intelligent. Our coach is a 2002 with what I'm sure is an inexpensive OEM "IOTA" brand Converter/Charger/120-VAC Breaker Box/12-VDC Fuse Panel. I was SURE it'd boil the battery (single 12 Volt GP27 Walmart Deep Cycle/Trolling Motor battery) but it does not. Our first Class C, had the common 1980's MagneTek, and it boiled batteries big time.
