The only way you will know for sure how much payload you have is to load up your truck with everything you take camping, full tank of fuel and all of your family. Then go the scales and weight the truck. Get total weight and also for each axle. Once you know how much you actually have on the rear axle you can subtract that from the sticker on the door.
Going beyond that is a personal choice.
The forest river website shows the pin weight of that camper at 2080 lbs. Of course that is before you put all of your things in it.
