I own this setup.
2016 F350 diesel dually.
2016 Grand Design 385TH tri-axle.
I have the Trailair Kingbox with inflatable tire and shock absorber (must have).
I use the Reese Elite 25K hitch mounted in my bed. I suggest you get some airbags on the dually as they made a huge positive difference for me.
I sometimes need to look in my mirrors just to remind me I'm towing!
Awesome uphill...great braking...no sway.
I am positive I was WAY overweight last summer driving from MN to MA with zero regrets and zero hassle!