You'd need to check the water level at least once a month for sure.
I killed a battery this way. Took a couple years, but on a trip we stopped one night in a state park with no hookups and discovered that the battery, while showing a full charge, was actually incapable of delivering more than about 30 seconds of light on one fixture/two bulbs inside the trailer. The battery had sulfated, and while showing full voltage, was none the less dead as a door nail.
I installed a cut-off on the battery, and now leave the trailer off shore power, the battery disconnected, but on a Battery Minder, which is supposed to prevent sulfation while keeping the battery fully charged.
