OP, you'll always get a few replies from people who don't read your post completely. Just ignore them.
Thank you for letting us know that even a properly loaded trailer with sufficient hitch weight can sometimes sway. Applying trailer brakes (not vehicle brakes) was certainly the right reaction. You did well.
May I ask why you prefer friction bars versus something like the Equal-i-zer or Reese Dual Cam? I've read that those friction bars will act differently when they get wet (as yours were, running into that storm) than when they're dry; have you found that to be true?
On a tangential matter... I wonder if I should give my wife a sway bar? Her back end sways with every step! (Don't tell her I said that...) :B