I'm fairly sure that the charging wire in the 7 pin connector isn't going to do much, if anything, for you. For all but the smallest DC-DC charging system the wire gauge is simply too small. Vic's threads on 12VDC power have all of the info in them, maybe too much info, that you're likely to need.
The Exec Summary for direct Alternator charging:
Wire gauge between camper & truck 6ga.+
Breakers or fuses at both batteries.
Automatic Charge Relay or Voltage Sensing Relay
Anderson forklift connector
Optional: Battery monitoring system
The Exec Summary for DC-DC charging:
8ga min (some *might* be OK with 10 ga.)
Breakers or fuses at both batteries
DC-DC charger (dedicated or multiple input solar charge controller)
Anderson forklift connector or Power Pole connector (depending on wire gauge.)
Optional: Battery monitoring system.
Some opt to go with the DC-DC system whether they need to or not. Other's vehicles have "smart regulators" on their alternators and the DC-DC type system is their only choice.
Some here will disagree with me on saying that the battery monitoring system is optional, and to a degree they are correct, but I do not see it as an absolute must have. Certainly a very nice to have and very useful in tuning the system, but not an absolute requirement.