Battery life compltely depends on usage. If you are gonna use the tv, radio, lights, it will run dead. (Usually at 4 am).
Don't ask me how I know. Most people that dry camp use as littl eelectricity as possible or a generator.
I've noticed an increase in solar panels at campgounds that I frequent. But I still prefer full hookups.
I'd recommend charging up your battery, travel to your dry campspot, and enjoy your trailer. just check your battery meter often, if it gets down to 1/4 then plug the 7 pin into the truck, start the truck and let it charge for a few minutes.
Whoever told you that a battery is "dead" at 50% doesn't understand what a deep cycle battery is designed for.
20XX 3/4 something TBD
2010 K-Z Spree 318BHS LX