Sorry for you troubles - any chance you have photos that you can share? Might help others down the road Did you buy it used BTW? How did the previous owner car for the unit (miles driven) if you did. I see you joined Nov 2021
Lippert fully covered the frame crack repairs (including new sub framing and cross members) on my 2018, and GD pitched in with new coroplast (belly fabric).
Did you set up a case # with GD or Lippert? While I don't know you or how you approached the issue, sometimes being pleasant and calm and working with folks goes a long way in negotiating things.
Last have you ever scaled your trailer loaded? A lot of folks are overloaded and don't even know it. This can add to frame stress. Not saying your were, just passing information to others to check.
Good luck finding a better brand. Lippert builds the frames for most brands and the other working components are the same too.