My 2011 F350 and Ascent camper have about one inch. I take mine on gravel roads to camp off the beaten path all the time. Never been a problem. I think there are a few factors here; the suspension on your truck, how much your camper flexes on the overhang and how well its tied down.
*2011 F350 SRW CC/LB/PSD - Mods: Custom overload springs with custom early engagement blocks~Firestone Airbags~Hellwig Big Wig Rear Sway~Rancho RS9000XL~Bilstein Steering Damper~19.5" Hankook DH01'a on steel wheels.
*2012 Chalet Ascent S95R Camper