If you can't find a reason for the battery drain....
It's possible the battery has gone bad. The newer batteries have thin plates which can break due to road vibration or bad bumps. I had a battery go dead and took it in for testing. The load test showed the battery was good. I charged to full charge and the next day it was dead again. I took it back to the same place for testing and this time it tested bad.
Is it possible they may have given you an older battery ? One that had been sitting on the shelf for a year or more. Most RV dealers take off the batteries and propane tanks while the RV is for sale on the lot to prevent theft. It might be possible someone grabbed one from the warehouse without paying attention to the condition or date.