Sometime back I remember reading on here or some other RV forum that Lippert Industries advise that owners of their framed units to not travel with Fresh Water in the holding tank because it contributed to frame failure.
Though you have not listed the make,and model of the unit, I think you are screwed.. I'd be taking it to a local weld shop and having them go over everything. Lippert is known for substandard welding. When your 'welders' were slinging burgers the day before and are now welding with a glue gun (MIG) with little to no experience concerning weld penetration, proper grounding or things like wire speed and correct amperage, you get faulty welds. Fact of life and the labor market too.