It doesn't surprise me that Keystone would have no "expertise" in how to repair a 12 year old trailer. They have "little expertise" in how to repair last year's models.....
That said, you can download the 2007 Outback brochure here:
https://www.keystonerv.com/media/2484/outback-2007.pdf in that brochure you'll see a couple of drawings that depict how the frame is constructed and might give you some insight into what you'll need to do to repair your damage.
Good Luck and although you'll be "pioneering a repair" there are probably others who will benefit from your experiences, so please consider posting your progress as you work on this project and post photos/comments that you think might help others with the same or similar trailers.
Again, GOOD LUCK !!!!!