It will be on the backside of one of the spokes, not visible unless the wheel is removed. The Keystone site lists the 305 as having 6,000 lb Dexter axles, so that would indicate they would have 6 lug wheels, which will not likely be 110 psi wheels, most likely 80-90 psi rated. The tires specified are also only E rated.
copied from the specs for the current year:
6000 LB DEXTER E-Z LUBE AXLES WITH SELF ADJUSTING BRAKES (305, 310, 344, 345, 330, 331)
Bob & Becky
2012 Chevy 2500HD D/A CC 4WD