[twindman]

You don't need anything. Just remove the battery cable for the time it isn't being used. I leave mine sit for 5 months - often longer - and the batteries will still raise the front jacks when hitching up. Just make sure it is fully charged when you store it.
A handy and useful item is a volt/amp meter. There will be other times when it is nice, but you can check the battery voltage. If you are new, you may not realize that a fully charged battery is at 12.73 volts, not 12. And wait a few hours after it has been charge to check. Just plug it in for 4-5 hours with a standard drop cord and it will charge up via the convertor.
Happy camping.