i put 2 batteries on my 23SS. my '07 has the battery in front of the propane tanks. i think yours has the battery behind the tanks.
i would recommend 2 6v golf cart batteries if you can do it. they will last a lot longer than 2 12v batteries.
i had clearance issues with my tailgate and electric power jack, so i had to stay with the shorter 12v batteries.
i just used battery cables bought from an auto part store to hook them up.
12v are hooked up parallel and 6v are hooked up in series.
i just bought two cables to hook 2 of the batteries' posts to each other and used the two cables from the trailer for the other 2 posts.
here's a pic: