I've been refreshing my high school metal shop skills doing patch work on my '66, I can weld but definitely not a professional..I have the same welder you do, heres some things I have learned that may help...
Like others have said, old trucks have really dirty, rusty metal...Clean all the areas where a bead is going to go till they are shiny metal, and don't forget to do both sides of the metal, not just the side you see when you are welding. You should be spending way more time prepping than actually welding.
For tricky bits, do a "dry run" first, moving the gun through the weld without any power on so you can get a feel for what you will need to do to line everything up.
Also, make sure you have a good ground as close to the work area as possible...The ground clamp on that machine sucks, I keep meaning to get a better one at the welding place, but in the meantime, make sure you have a nice shiny bare metal to ground to. I also got one of those magnetic ground posts so I usually just grind a bare spot 4" or so from my work area and use that to ground there...It also really does seem to make a difference if you get to far away from the ground...
Finally, don't get impatient. Lots of small, short welds, almost tack welds are your freind. If you blow through, don't worry about it. Move to a different spot, come back later and fill it by a bunch of small bursts around the edges. If an area gets too hot, it blows through easier...
Finally, just relax. If its [censored] you off, take a break and come back later.
You'll get it...all the hassle and agravation is worth it now that I can see a whole new floor instead of the chantilly lace of rust I had before, it feels really good to have done it myself.
