Probably the most sure way to disconnect the batteries is to take one of the leads off--this would also be a good time to clean out the battery compartment--most units can really use a good cleanup in the battery section if the previous owner has not been kind to it. There are also battery disconnect switches that will mount on one of the battery posts to help in subsequent disconnects.
There is usually no end to upkeep on RVs--and getting the batteries up to par is about the most basic step. Take them out, get them CHARGED and CHECKED for condition, clean up the compartment/connections and put some of those red/green corrosion preventer washers on each post. Once you have all that done, and the disconnect installed, you should always have good power left when you return.
Enjoy the new fiver.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired