Your camper is set up for 120 Volts 30 amps - Your truck is able to put out either 240 volts 30 amps on a single circuit or it can simultaneously power two 120v 30 amp circuits. This is what the A and B means - if you are powering 120V circuits, A and B will each reflect one of the two 120V circuits. If you are powering a 240 V circuit, A and B will each reflect one leg of the circuit. I'm simplifying a bit but hopefully this makes sense.

My Airstream is set up the same way - I see a few hundred watts while towing to run the refrigerator, and I can see up to the full 3600 watts when camping and using the microwave and air conditioner simultaneously.

I would add one small correction to one of the above posts - if you are seeing your trailer connection show up on B, and you want to run any other devices by plugging them directly into your truck, plug them into A - you have another 3,600 watts still available on A even when your trailer is plugged in. If you plug other devices into B, they will be competing for power with your trailer.

I fully agree with the above poster that powerboost is game changing for dry camping. We also keep the trailer powered up while towing using our front power inlet on the airstream - saves propane for keeping the fridge cold.