No way you should need airbags on a dually with a 7k trailer. Airbags INCREASE the spring rate. High spring weight makes for bumpy ride. Make sure you have good shocks.
Your tongue weight should only be about 700-1000lb and that should not be bottoming a dually.
For the best results:
Take your truck to the scales and jot down front and rear axle weights empty, and total weight. You will use this number a lot, so write in your glovebox or door jamb. Also write down your bumper height unladen.
Hook up the loaded trailer and get all three axle weights. Do not use the equalizer bars yet.
Get the rear tires on p'up to read an increase of 10-15% of the trailer weight. You do this by adjusting the load fore and aft in the trailer.
Now tighten the equalizer bars until the bumper height goes back to stock height.
Check to make sure your front tires are not overloaded. If they are, then loosen the equalizers until you are good.
We use a 3500SRW (8120 unladen) to tow a bumper pull 12-14k lb trailer. Equalizer bars, tongue weight, shocks and tires, are all very important for a smooth ride and safe emergency handling.
My bet is you have too much tongue weight. Tightening your bars is not a replacement for correct trailer balance.