I usually add air in mine after connected to the truck and air up till it is level...never even put an air gauge on it...just air till level...
'11 F150 XLT Red Candy Met. Ecoboost 4X4 Screw 5.5', Max Tow,Reese R16k 5th wheel hitch,Ride-Rite Air Springs, E Rated Tires, Extang Cover
'13 Keystone Cougar X-Lite 29RES,triple slides,Mor/Ryde suspension, Reese 5th Airborne Sidewinder, 16" E rated tires