One tip that might help. When GTA welding thin aluminum, many will start with very low amperage. The nature of Al is that it conducts heat away quickly, so may be difficult to get a puddle going, then a small weld is possible, but soon you blow through. Try starting a bit hotter than you think normal, but move quickly to stay ahead of heat buildup. Manipulation of the filler to help absorb some of the heat is also a good tip.