Almost all 12 volt wet cell batteries are not true deep cycle. 12 volt RV/marine "deep cycle" are actually hybrids so they work well for starting. If you want true deep cycle in a wet cell battery your best bet is converting to 6 volt golf cart batteries. They are readily available.
If you don't have a battery disconnect, get one or keep a battery maintainer hooked up when in storage (both is best).
Get a good multi stage converter (like Progressive Dynamics). It will charge faster.
Consider what electrical loads you have in the RV. Convert to LEDs for lighting and put switches on things with parasitic loads (like stereos).
....and then there's solar.