If I ran dual alternators on a truck camper rig (and I have thought about retrofitting on my 2015 Ford), I would isolate the second alternator so that it is only charging the camper house battery, and add an external regulator. The external regulator can be set up to properly charge AGM batteries. Probably the best way to do this is to buy an aftermarket alternator from Balmar or other marine supplier, and the mounting parts from Ford. That would be the premium truck camper charge setup.
But with two solar panels on the roof, I never seem to have to worry about charge - the charge wire from the truck isn't even hooked up.