Jim, I have welded 4130 with MIG and flux core wire. Nothing on an airplane but various parts of the kids go-kart, jigs, fixtures, etc. Like you, .032" or 1/32 is the thinnest base metal as I have done. With a little practice, I would definitely consider welding a steel tube fuselage. Many years ago a friend welded a fuselage with MIG but I think he used hard wire. He never completed the project so I can't tell you how it turned out.