Have not had this type of problem, but I agree that you should contact Jayco and ask for suggestions on how to fix. The other thing is that if it were me, I would consider using something like 3/4'" X 3/4" box aluminum tubing for your DIY repair supports instead of angle. It is much stronger with only slight weight increase, and would be better in high traffic areas, IMHO. Repairing from the underside is also a good idea, assuming you can access all affected areas.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.