You should get better and longer service from 2x6 deep cycle batteries. Don't believe there are any real 12 volt deep cycle batteries. However, if you are going to always be plugged in when using the fiver, then probably the 1x12 will work ok.
I prefer storing with slides in, don't know if I can say why.
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