My first guess would be a light is on somewhere in the unit. Is there an under hood courtesy lamp that might not be shutting off when the hood is closed? Some use a mercury switch to shut off, when the hood is closed, and I had an older Chevy product kill 1 battery and severely beat up another before I noticed the light shining out from under the engine compartment on my driveway one night. The other "lights on" places might be in one of the storage compartments, but I would think they'd run off the coach batteries. That does seem like a lot of amps for even an incandescent light or two. It must be something else, like a fan motor or something similar.
Just some guesses.