Sorry for your frame issues. Is that the factory pin box or was a extended pin box added?
On my Lippert frame on my F40SPTS, it has plenty of bad welds and lots of "undercut" telling me the welder was inept and under time/production pressure.
I was told by a Forest river supervisor( while at the Rialto,Ca factory in 2006) while my F40 SPTS was in the factory for a second volley of repairs during my first 6 months of ownership that, their units were not engineered, but drawn up and put together on the line. This supervisor said that at least when he worked for Fleetwood, they engineered their units...
That might have something to do with it..
Hopefully Berkshire Hathaway or LCI will take care of you.