In my experience the factory weights do not include everything that goes inside a camper, like an AC unit, a battery, storm windows, roof rack, ladder, propane. They say they do but the sticker on my camper stated 2700 lbs. and when I picked it up from the dealer and took it to a nearby CAT scale the weight came in closer to 3200 lbs.
Adding in another battery, a solar charging system, steel rolling racks in a cabinet, and the weight when we hit the road is around 3700 lbs.
With a 11' camper the dry weight is going to be 1000 lbs. heavier anyway you cut it and that takes 1000 lbs. from the equation that could be used for a generator, tongue weight of a trailer, fully filled holding tanks, and other "necessities. The 11' provides a dry bath and that is very appealing to some.
More weight also impacts tire wear and fuel economy and accelleration on the highway either to get onto a freeway and safely merge with traffic or passing a slow truck on a grade.
The added length also makes it tougher to fit into some campground spaces and may create problems in later towing a trailer or adding a storage rack at the front of the truck.
I would take the new GM fully boxed truck chassis (introduced in 2011) for a super heavy camper as it will handle better without all the flexing. Some modifications or upgrades will still be needed but if you look at what people with very large and heavy campers have felt necessary to do in the way of modifications you will have an idea of the price paid for such a camper regardless of the truck it rides on.