I think at this point I would take photos of the "repaired floor" and send to F.R. Let them know you are disucssing your problems on the fourm with other F.R. customers. Many of whom are upset with F.R. and their dealers workmanship. If nothing else it helps you vent and sometimes the squeeky wheel syndrome works. Since you trailer is brand new, tell them you want it replaced.
BTW our Flagstaff had the metal strip covering the seam joint on the underbody covering held in with wood screws that went into air also. It all fell off.