I've had the converter fail while camping. Back then, I didn't bring a stand-alone charger with me. But I did have my jump pack, which had a sealed lead acid battery inside. I only needed power for one more night, and this worked fine, though looked a little odd.
Now I carry my old Diehard (Sears) 12V automatic battery charger. I used this to keep batteries fully charged for several years in my garage.
While on another camping trip, someone with a new 5th wheel asked if I could help troubleshoot their battery issue. Dead converter. I loaned him our charger for the several days we were in the same park. Turned out he was one of the folks that reviews campgrounds for Woodalls. Gave me the latest campground guide when he returned the charger. That said, yes, a stand-alone charger will keep your camper going. Mine will only supply up to 10A continuously. But with it charging all day, with little 12V usage, any spikes at night will be supplied by the charger AND the recharged battery bank.
The jump pack lasted for years. Every few years I had to replace the internal battery. The case eventually started cracking. Finally threw it away. I now carry a DBPower lithium jump pack in each of my vehicles.
https://amzn.to/2Z7FW5p
