Even with the disconnect switch on the off position, you will still have a small load. On my motorhome, the propane detector is always powered, even when the 'disconnect' switch is off. A few other little things too, like the electric steps and I don't remember what else offhand...
For long term storage (anything more than 2 weeks), I pull the cable between my batteries (dual 6 volters).
And I'd highly recommend the link time2roll posted. Even if you are not mechanically/electrically inclined, understanding the electrical ins and outs of your RV will be very worthwhile. That page is a classic, written a long time ago and still stands the test of time.