Very common. Part of the problem is the steps when used often. Then you have those small and fantom drains on the chassis. Mine would take about 5 days.
You have 3 ways to deal with this. Get a manual battery disconnect switch. Keep it on a battery tender, or get a Trik-L-Start.
http://www.bestconverter.com/Ultra-T...art_c_124.html
I leave my coach plugged in all the time to maintain the coach batts. The Trik-L-Start connects between the coach and chassis batt. So anytime you are plugged in (or run generator) your chassis batt is kept charged also.