Check your ride height first before changing anything. Just measure the gap between the upper A arm and the stop right below it you should have about 1.5 ins or more. If the A Arm is resting on the bumper stop with no space in between I would replace them with new HD springs. If you have some space you may get away with just adding new air bags. How many miles are on the MH? The bags will only add another 500 Lbs capacity when fully inflated. As others have said new shocks won't increase the ride height.