Greg,
I don't know much about your year/model coach. So, I don't know if it's got Chassis battery charging capability while being plugged into shore power or not. And, you don't say whether you're plugged in or not. I'm assuming you're not. As you most likely know, there is "parasitic" loads on chassis batteries. Things like radio memories, Gas detectors, Engine and transmission ECMs use a tiny bit to hold memories of data and more.
I don't even know if your coach is a diesel or gas. Do you know if you have chassis battery charging capability when on shore power? Winne and Itasca didn't prior to early '06. After that, the factory started installing the infamous "Trik-L-Start", chassis battery charging system. Many have purchased that same system for installation on previous years of Winne and Itascas as well as other model coaches of both gas and, diesel.
But, all this really pertains to shore power. If you don't have or, cannot get shore power while your coach is in storage, then, other measures have to be taken. One, if you don't have "Battery Disconnect" switching, for either set of batteries, then, I might thing about getting some installed. If installed correctly, they an eliminate all your battery drain while in storage.
Now, another thing here. Are you sure you've got all items, i.e. lights, compartment lights, radios, bathroom fans, ANYTHING, turned off before leaving the coach in storage?
A small but, fairly accurate test to see if there's anything on or, a possible draw on the system would be to, remove the negative battery cable from the chassis battery, and, install (in line) a 12V test light between the cable and the negative post. If that light lights up, something's on or, there's a draw someplace in the chassis battery system. If it doesn't you're still not out of the woods. If you put a VOM in between those two items and it reads ANY voltage, you're experiencing a smaller draw than what would be needed to light up a test light.
But, the next time you go out to run the coach, as has been stated, run it for at least 20 to thirty minutes, preferably at about 60 mph so the charge rate is as high as possible and, for as long of duration as you can tolerate. That will assure you have a good state of charge prior to shut down at the storage yard. Let us know what you find out will you?
Scott
Scott and Karla SDFD RETIRED2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing KI60ND