The camper has items that constantly draw power from the batteries. Most single battery campers will go dead in about 3 days and once a battery is fully discharged, it will have permanent damage which is evidenced by reduced capacity.
Having a battery selector switch is an easy way to disconnect the battery without pulling the lug terminal off of the battery each time you want to connect or disconnect.
How to do it:
Buy cable, cut to size for location of switch, crimp or solder connector to battery cable, attach to switch and your are done. Run wire from + terminal to switch.
My fifth wheel has 3 battery banks and each one is switched.
Recommend you use a Blue Sea Systems switch which are easy to rotate and well made. Perko are good switches but wife has trouble rotating them.