Payload sacrifice going from regular cab to crew cab

Pretty much every one ton dually made since the ‘70s uses either a Dana 80, AAM or Sterling 10.5 rear axle. They’re all rated between 10,000 and 11,000 pounds.
Just go get any dually and you’re fine to haul a camper.
Forget all this adding hot e weight of the sunroof or the fancier sound system or the rating sticker, which is a taxable license class weight not a truck safe capability rating.