On a brand new truck that's likely $50,000 plus what's another $400? I'd get the duals for sure.
Now, will it help charge your camper batteries? Not without significantly larger wire feeding them thru a separate Anderson style connector or one like used for tractor trailer lift gates. If you're going to be putting hundreds of AHs of battery in the camper/truck I would upgrade the wiring to match.
For my use I typically have stereo amplifiers, amateur radios, inverters, etc. along with the RV. I will absolutely be getting dual alternators on my next new truck.
