I am currently doing what you are asking with great success and no troubles whatsoever the last 8 years.
My Truck Alternator to Truck Camper SETUPI have two AGM group 31 batteries in the TC and I recommend having an AGM starting battery in the truck for better electrical matching.
I have a 160 amp output alternator. I imagine the TC batteries add as much as 22 amps demand to the charge system when discharged overnight say 12.3 volts and very little demand once fully charged through the 4 gauge wire direct off the alternator and controlled by a constant duty solenoid.
Works great, charges fast, Trouble free, have never blown the 30 amp inline fuse.
Go for it, don't hesitate.
