News you can use?
-- A major drawback with some (most) factory wired 7 pin connectors is that the gauge of the wire is probably too small (i.e. gauge too small) to pass enough amps to charge a camper battery during the time that the vehicle is running. This is especially a problem with lead acid where getting a full charge is essential to long battery life.
-- A second issue is that the charging profile of your vehicle may not be appropriate for your camper battery. The new "smart" alternators increase the chances of this. A DC-DC charger can fix this problem.
-- Sadly, because of the question of wire gauge, simply mounting a DC-DC charger on your tailer and plugging it into the 7 pin connector may not work because of the wire gauge and length. But, a small enough battery and a short enough run and you may be fine. You need to check the documentation of your DC-DC charger. (I use REDARC and they generally want a minimum of 6 AWG.)
Again, hope this is helpful.