Quite often the tank mount isn't installed till the unit arrives at the dealership. Regardless of where it's installed, they nearly always use self-drilling sheet metal screws. Instead of having the screw gun used for the install torque-limited, they go at them full twist. The end result is a structurally weak connection and the heads pop off in little time if not instantly due to the stress.
Because the threads of the screws are coarse, and the thickness of the frame tube thin (relatively), you can use a hardened punch and a ball peen hammer and knock them right through into the frame. Replace them with a larger diameter, thread cutting (e.g., McMaster-Carr
) screw of the needed diameter.