I'd also clean and check all battery connections, including ground connections. Make sure any lights in compartments are off, TV antennae amplifier off, etc. You could pull all the fuses and test to see which one is drawing power.
In general, if the RV is parked more than a few days, disconnect or use a battery disconnect switch or plug in to shore power. There are many small draws of battery power, from radio and engine computer memory, CO/LP detectors, etc.