Bluecat, since you have a lower number of posts, I'm going to assume, maybe incorrectly, that you have a new RV. If so and the battery is new also, just do as everyone above advised. If you have bought a used trailer and the age of the battery is not known, understand that having two batteries of different ages hooked together will limit the batteries somewhat by the older battery if it is not in great shape. I only mention this because If that is the case, It may be better in the long run to get two batteries new and you know they are of the same age and same strength.
Good Luck in your project. It's worthwhile for those that spend time of grid!
2020 Chevrolet 2500 LTZ, 2019 Forest River Wolfpack 23Pack15, 2014 EZGO Golf Cart.