If you leave your trailer plugged in a lot, the best investment you can make is in a smart converter or inverter/charger with the smart charge technology. You will pay for it with the first set of batteries burned up with the constant voltage converter. I have added water to my batteries one time in four years.
2003 Dodge HO 6 speed Laramie Dually, Jordan controller, RDS fuel tank, Air Ride 25K hitch
Carriage 36' fiver, Onan 6500, Prosine 2K inverter, 3 slides, MORyde IS and Kingpin