Why Truck Camper need a air bag? Do I really need it?

Your truck and camper will probably be fine.
It only needs air bags if the camper weight makes the rear end sag too much. When that happens the front headlights will point upward too much and at night it will blind other oncoming drivers.

Ram and chevy have stiffer springs than Fords - it's usually the Fords the sag over the rear axle. Your truck should be fine.