Very frustrating situation, going to blow some steam!

First off, if you want to criticize him about his long post/no paragraphs, PM him as posting it here adds nothing on helping his problem.
While not a fan of lawyers, on a 09 trailer that you bought new and are still having problems you need one. You have done more than most to try and fix a weak frame. Only a lawyer (on contingency) can get you out of this problem after owning it for five years. Good luck and it sounds like the DW is doing better.