tinyphil reported the same problem with his 2007 Wildcat here, six months ago:
It does not appear that Forest River or Lippert have done anything but make the stock "out of warranty" denial to tinyphil for such major hidden defects. His last post in that thread was dated November 2010. Perhaps Forest River will contact him now, resolve his frame issue and get him back to tell us about it.
All RV manufacturers produce lemons, and it appears tinyphil had one of those. That is one of the risks we take in buying RV's. Major hidden structural defects of the sort you and tinyphil mention, however, pose a whole other category of risk - a direct and immediate threat of major injury, and even fatality, in avoidable vehicle accidents while towing.
This is definitely something to bring to the attention of government regulators, as well as lawyering up. An RV manufacturer's failure to resolve life-threatening hidden frame defects would be unforgiveable, so Forest River's resolution of your problem, given tinyphil's very similar report, has headed off what would otherwise be an unmitigated public relations disaster for them.
These sorts of hidden frame issues are very dangerous to buyers, as well as threatening the total loss of their investment. A manufacturer's refusal to redress hidden structural defects is clear and convincing evidence concerning its willingness to redress other defect issues, and the manufacturer's institutional culture overall.
Forest River did the right thing with you. I'd like to hear from tinyphil soon.