I've only recently started welding and to date it's only been box section. My welds I'd say looked reasonably sensible so I thought I'd try something a little more challening....and a bit thinner. I'm currently restoring a car and decided to tackle the welding myself. It was a bit hit and miss at first, some of the welds weren't too great and when they were solid they were still a bit messy. I wondered if it was because I was welding with flux cored gasless wire. I tried my hand on the wings and obviously the welds had to be tidier and invisible as you could see this area. I think the welds turned out OK, but they took forever and I had a lot of issues with burn through and pinholes. It only really started to work out when I used a copper heatsink. I've now changed to normal wire and C02 but not tried it yet. Any tips and pointers to get decent penetration without blowing through??