You are not going to get a lasting fix until the Lippert frame issues are fixed and that nearly requires a total disassembly of most of the RV. Would be cheaper for them to have replaced your Montana and you are not the only one by far who has had frame issues with Montana's or Keystones with the Lippert frame. Many threads on Lippert frames breaking/issues on this forum alone for years now.
Your problems are beyond severe and totally unacceptable and they'd started long before your Keystone one year warranty was up. If your documents etc can prove your many repeated problems in writing, a good lawyer should be able to help you big time and make very short work of true repair or replacement and perhaps all the cost you have incurred due to the Montana problems too. Don't give up!