Not a clue as to what Fabshield is, but solid wire with that C-25 (argon and CO2) shielding gas is the only way I have ever run a bead on light gauge body steel. As Roger pointed out, several tacks, and depending on the thickness, will determine how long you can run that tack. I generally try for a half inch or so, skipping 2-4 inches ahead then back to allow some cooling and minimize distortion which will always happen to some extent. If you are trying to run a continuous bead several inches long you will eventually "blow through" with flux core or solid wire. And TIG - itwill blow through as well when you localize too much heat