I pull a 29' camper with a Tahoe using the Elite EAZ-LIFT hitch assembly. I started pulling the trailer with just one sway bar and it felt a little loose around semis at highway speeds (60mph less than 10mph winds).
I found a few internet threads that say trailers over 28' are recommended to use two sway bar setups. So I then added the second sway bar and I was able to pull it safely at 70-75mph highway speeds with low wind (less than 10mph).
I am now sold on the dual sway bars when traveling on the highway.