Need suggestion for trailer wiring

I’m not sure I get what you mean either. If you’re using your 7-pin for a trailer and you aren’t plugging the camper in because of that, you can just put a 7-pin in the truck bed for the camper. I thought everyone did that.
And as for charging the batteries, running a separate 2-gauge or larger + and - from the truck batteries to the camper will get real charging current to the camper, the stock tiny wiring will “trickle charge” at best. Use a separate heavy duty plug to disconnect, Anderson plugs work great.

The alternator makes plenty of power, it’s never that. It’s all about the wiring being adequately sized to get it where it’s going.

My Ford has dual trailer plug, so when I pull utility trailer, I plug it into 4-pins when camper plug goes into 7-pins.
You can make an adapter like that if you don't have it.
For both 7-pins Here is ready adapter.

If the only 7 pin is plugged into your trailer how are the campers marker and turn signal lights powered?

You can add a second 7 pin to your truck. Modern trucks prepped for 5th wheels have this from the factory. On plug in the bed, one on the bumper. You could make up a splitter turning your single 7 pin into a Y with 2. The effective charging from a 7 pin is minimal and depending on the alternator load now with the trailer, camper and the truck don't expect much in the way of charing to the camper battery especially at night with all the lights on.

You could run a larger dedicated line from the truck to the camper which would help with voltage drop but again your stock alternator might be a limiting factor for getting a good charge.

If I'm following your questions correctly, there shouldn't be any difference. Your 'hot' wire (should be red) is constant 12v. Doesn't change, whether it's a trailer or TC.


On that note:

Not all 7 pin RV plugs are wired the same. It's a PITA. We switched over years ago to std 7 pin (round). Matches everything including commercial, and the plugs are easier to use and change out.