Two friction bars ARE better than one. Using two bars gives you almost 1/2 as much force maintaining a trailer in a straight line as a low cost integrated system like Reece Duel Cam or Equalizer. My advice is go for a better system rather than more of a weaker system. I have towed many thousands of miles with a friction bar (and a small trailer). For anything over about 25 feet, go with something better.
Concerning the use of air bags, they really have no useful function in towing a conventional trailer. All they CAN do is prop up the rear end and they have ZERO ability to replace lost front end weight caused by pushing down on the rear of the tow vehicle. It's this loss of frong end weight that causes MANY of the towing problems people have. You CEFINATELY need a WD system and loose the air bags. They're GREAT for towing a 5th wheel or hauling a slide in camper. Conventional trailer....not so much.
Good luck / Skip