Stored on a site without power.. For up to six months (Though I'd like to limit to 4) Make sure they are FULLY CHARGED, then. operate any disconnects provided and then Lift the negative cables off the battery, While you have 'em off put something black on them,,, Paint, Tape, wire loom (Put red on the positive wires)
Stored on a site with power.. IT depends on your RV. More specifically the power converter.
Magnetek 6300, Parallex 7200... Do as above and connect a Battery Minder or Battery Tender to the batteries and feed it power.
Progressive Dynamics Intella-Charger with charge wizard (Optional or built in), IOTA with IQ-4 technology, etc. plug in rig.
The difference.. The first (magnetic) is a single stage converter with very lousy regulation, the 7300 has better regulation but is still single stage, teh 7300T is the minimum acceptable charger (it is two stage, not the T, for Two stage).
The others (PDI with wizard or IOTA with IQ-4) are among the best of the best 3-stage converters.