+1. 

279 is basically the same as the 281 lbs listed as tongue weight on the FR website for the 189. That number would be for a dry trailer, no water in any tanks or in the water heater, no battery, and nothing in the trailer at all.  Its hard to see how that could be the actual tongue weight of a loaded trailer unless maybe the gray water tank was full or there was some other really heavy stuff loaded aft of the axle? 

If that number is right then its understandable that you have sway as the empty weight of a 189 without any options , batteries, water, or other stuff is listed as 2792. A/C, battery, and water in the water heater alone are going to add a couple hundred lbs, so you would be about 9% tongue weight or less. 

What is the full-up weight of the trailer? Multiply that by 0.11 to get an idea what it should be.

For example, for a gross trailer weight of 3850, the tongue should be "around" 423 lbs.

Greetings:

Do a little research online.  WDH come in several configurations.  The torsion bar type using chains require you to disconnect the bars before backing up, and are priced a little lower.  Other types use bars that slide back and forth or like my EAZ-LIFT Recurve R3 has a hitch that swivels.  They all work, I liked this design the best.  

Crankster78  R-179

It also comes in a trunnion style, which is a little more expensive.

We have the round bar, and it works great.

Greetings;

Buy a Weight distributing hitch with sway control.  It's worth the investment.  

Crankster78 R-179