Battery damage

Have you ever read The 12 Volt Side of Life?

Some chargers will not charge a very depleted battery. There is a threshold voltage that must be present for the charger to be operational. We don't know which charger you have. Using jumper cables from a running vehicle will increase the voltage so that any charger will charge the battery.

Did the battery become discharged because of the typical parasitic draws present in most travel trailers? A disconnect switch will keep that from happening.

If I was in your situation, I'd replace the battery with a quality deep cycle battery and install a disconnect switch (or remove a cable if pressed for time). Having to replace a battery while on the road can be problematic.

Every time you discharge a battery, even a little bit, it is "damaged" in the form of reduced capacity. Deeper discharges or longer periods without recharging result in more capacity loss. Eventually the capacity is reduced so much you feel the need to replace the battery. That day will come a little earlier than if the battery hadn't been discharged so deeply, but you may never even notice the difference.

Check the Specific Gravity of all the cells after charging.

Only time will tell if the battery is damaged beyond practical use. Charge it, check fluid levels if applicable and test it in the driveway before the trip. Be prepared to replace enroute if it doesnt last a night or two boondocking.

Damage will probabky not be immediately noticed. I would just charge it and use it until you notice it not holding a charge as it should. Coukd be years from now.