1st: Airbags will not improve your ride, but they will help to keep your truck level when towing your fifth wheel trailer. This is especially important if you are towing after dark.
2nd: Based on the numbers you provided, your new pin weight will be about 2,300 pounds (20% of 11,750).
3rd: When towing, always pump up your rear tires to their max rated pressure (80 pounds), other wise you will be short changed on their weight carrying capacity. Lower air pressure means a lower weight capacity. When not towing, many of us reduce the rear air pressure to about 60# in order to gain a softer ride.
Lastly: Airbags will not help with porpoising, which is generally caused by insufficient pin weight. You most probably had that issue with your last trailer because of the rear kitchen. If your new rig has the kitchen over the axles, the problem will go away.
Good Luck