Lets establish a couple things before a recommendation.
Usually motorhomes (intent of this post) have at least two group 27 batts. They are usually strapped, with multiple terminal connections, so removal in this senario is not a snap.
We'll assume your going to long term store them, as in a winter season lay over senario.
You would need to put a trickle charge on them, as batteries lose a charge even at idle (left in or removerd) over long periods of time. Faster discharge left in, due to parasitic demands in most cases.
So, assuming all of the above, the simple route is to hook up a cheap trickle charger (or spend bucks on a more expensive one, if that makes your comfort level increase) to just one of the batteries, as they are still connected and the trickle current will buffer between the two (or more) batts. A few things you need to do; fully charge your batteries and remember to check water levels before the storage period. ONLY add distilled water if needed, and check periodically over the winter, lets say once a month. A fully charged battery can withstand extreme low temperatures. This very senario has treated me well for years.