towing with Subaru Ascent

I can't see any reason why a sway bar would be bad. I think you have to keep in mind that rain (wet) will reduce the amount of friction supplied by the bar. And I hear that they have to be loosened before backing up sharply or the bar can get bent. Of course, the best protection against sway is to make sure you have at least 10% (but no more than 15% generally) of total trailer weight on the tongue; in your case you probably want 350 to 450 lbs actual hitch weight when loaded for camping. (If the fresh water tank is under the front bed, be careful! Water is 8.3 lbs/gallon.)

How long is the trailer? I'm guessing 20'?