A method of forming a tank with a stiffening assembly includes forming a fuel tank such that the tank wall carries at least a first and second insert, locating a connecting assembly within the tank interior aligned with the first and second inserts, the connecting assembly including a tubular body, a first coupler, and a second coupler, and coupling at least a portion of the first insert with the first coupler and at least a portion of the second insert with the second coupler to limit movement of the two wall portions relative to each other.