If your intent on doing it yourself. the best advice is don't mig chrome molly and the biggest thing to a good weld is slow and hot. If you welded sheet metal you know how easy it is to blow a hole. You want to flirt with this possibility all the time your welding. Warm it slow weld it slow and cool it slow. If you want to go faster you have to turn the heat up. like I say flirt with the hole. If you do that and have the right filler you have a head start. Practice, it's not a black art it's a skill.