Bottom line, run a heavy gauge, fused set of leads off of the truck battery, through a charging relay if you want automatic protection from discharging the truck batteries while plugged in and engine off, to a winch plug type plug in, to the camper batteries.
This is literally done every day to 1000s of new trucks that run aftermarket electrical loads.
If you need verification, take it to any upfitter business and either ask them or pay them to do it.
Yes charging rates on new trucks are now controlled through the ecm or bcm or some other m, but if your truck batteries are sucking juice, the “m” is allowing charging voltage to them. Period.
