Excessive frame flex in pin box area of fifth wheel. Forward left cargo door unlatching while towing. Vehicle is currently at Lazydays dealer in TN for inspection and TSB for excessive frame flex. Inspection has revealed major structural cracks and structural failure in upper deck steel frame structure. Vehicle has been deemed unsafe to transport and must be repaired in place or partially repaired for transport to factory. We noticed excessive deformation of the pin box and substantial rubbing of internal cabinets, etc upon return from a recent trip. Based of the damage, it would have been possible for the RV structure to separate from our tow vehicle putting us and others on the road at significant risk of injury or death. We saw indications of interior movement of cabinets and rubbing on walls for several thousand miles, but no indication of significant pinbox deflection until recently. Manufacturer has provided no guidelines or communication to owners to be aware of potential problems or to indicate things to look for that may indicate the vehicle poses a serious risk/hazard. Initial signs of rubbing inside the vehicle, and a loose latch and flapping of cargo door were observed in January 2024. We have video of substantial gap opening and movement of interior cabinets when taking vehicle off of stabilizer jacks and loading onto fifth wheel hitch of truck. Unable to get additional pictures currently as the RV is at the dealer for repairs. Will attempt to get photos of internal frame damage early next week if possible.