AS was already stated put in the maximum that the rear tires are rated for an in agreement with the manufacturer's recommendation for a DRW truck. For the front tires I would also use the manufacturer's recommended tire pressure.
If you are at the maximum the tires will do a better job in supporting the load and there will be less road sway from the camper and less sidewall flexing so less heat buildup in the tires - for a much safer ride. Nothing worse than a blowout with an inner tire on a DRW truck with a camper in the bed from both a handling perspective and in terms of having to change the tire.
Heavy duty trucks are engineered to carry a heavy load as are the rims and tires provided by the factory. No reason to not go with the factory specs. Not only safer but you will get longer tread life as well.
