Have you tried hitting the Battery Disconnect switch to see if that makes a prevents the battery from going dead? You should have two switches, one for the Main and one for the Auxillary Batteries. If you turn the one off for the chassis battery, this will obviously remove any drain to the battery. At least you will know something for sure something is draining it, and it's not the battery itself, even new batteries can be bad.
Keep in mind, just like modern auto's there's always a drain on the battery. Computer, clocks, radio, etc.
Does your '09 have the solar panel on top to keep the chassis battery charged? If so, then something must really be pulling current. As "skipwil" mentioned use a meter, preferrably a good digital meter that can handle 10-amps or so and measure the current load coming off the battery. Normally, I'd say it shouldn't be pulling more then an amp. But, I'm not for sure on that. If it is, something's not right, and you'll need to isolate it like "skipwil" mentioned.
Bob 2006 Monaco Camelot 40PDQ
US Navy Carrier Battlegroup 1959/1965
Winters in Florida, Summers in Blue Ridge Mountains