I use 50-50 solder and rosin flux to both tin and join the ribs. The key is not getting it too hot, once you burn rosin flux you have to polish back to brite steel. I use a medium sized iron combined with an acetylene(not oxy acet) plumbers torch. The torch heats the base metal just enough that the iron will keep things wet on the base metal. It takes some practice to get it down but it is not hard. On the ribs themselves I use just the iron, no torch.