I'd stick with the golf cart batteries; they are true deep cycle. For capacity, compare Amp-hours at 20 hours (apples to apples) discharge; obviously, one AH at 6V is equivalent to one-half AH at 12V.
Most residential refrigerator installs have 6 golf cart batteries standard; and you will want to have Automatic Generator Start in your system as well. You're looking at major expense here.