What else can you do but charge them up hopefully using a smart charging device. If they take a charge which I believe they will, then follow with an equalization routine. If your RV converter doesn't provide multi-phase smart charging it would be a good time to upgrade.
Obviously, it never hurts to by a high quality battery such as Trojan, we buy our 6 volt GC2 batteries from Samsclub for cheap and know nothing has more relevance in their over all performance and longevity than how they are maintained and re-charged.
We leave our rig plugged in 24/7 when stored in our side yard and our smart charging converter keeps them in tip top shape, although we use a portable B&D 40 amp smart battery charger for occasional equalizing where voltages exceeding 15Vdc are required.