A disconnected fully charged battery will have a long shelf life just sitting there. They do need to be checked ocassionally and of course if the charge is dropping back then do some trickle charging... Leaving my batteries hooked up will drain down rather quick from the parasitic drains inside the trailer... I switch them completely off-line and let them sit on the trailer tongues... Being fully charged they will not freeze up on you...
Being no 120VAC power at the camp site almost makes you bring them home with you or setup some sort of solar panels to trickle charge them. If the charger is too much this will boil out the battery fluids over time and destroy your battery...
Roy Ken