Best way to add load capacity is Supersprings and it is worth taking 10 minutes and giving their tech people a call. Tell them what you have and what you want. Adding springs keeps the truck operating as when stock and lets the shocks do their job as well. The other band-aid approaches do the exact opposite.
The E rated tires add to the load capacity but also there is reduced side wall flexing so you get better road handling as well.
Your planned camper load is well within what your truck can handle with added help for the existing springs. An anti-sway bar can also help, both with reduced sway and with a less harsh ride as impacts at one wheel are shared with the opposite wheel.