Battery draining issue

[Campy]

We went on a camping trip for over a week with no issues at all. Came home and parked the camper and in just a couple of weeks the battery is flat. I charged it up and turned off the master switch and dead battery again. Turns out the master switch don't turn everything off. Any ideas what could be a major drain or possibly the built-in charger itself, I had one in a class A fail and drain the batteries.