Ideally, welding everything in the flat position is the way to go - flat is the most efficient and easiest welding position. Of course, if you're welding on board a vehicle flipping it onto its side or roof isn't the most practical idea. There are 2 ways to perform a vertical weld: start at the bottom and work up (vertical up) and start at the top & work down (vertical down, also called "downhand" or a "wash pass") and they are NOT the same thing! Vertical up is just as strong as a flat weld of equivalent size, while vertical down is basically a cosmetic weld. Compared to a vertical up weld, a downhand has very little strength. Of course, it's easy to do and looks nice, but don't be fooled! On a structural steel job, if a welding inspector sees downhand welds they won't be too impressed and will likely require the weld be removed & redone. Vertical up welding can be difficult to learn, and although trying to teach "how to weld" over the 'net isn't too practical, here's a paragraph from the welding procedures book I carry in my work truck: Vertical Up: Use a triangular weave. Weld a shelf at the bottom of the joint and add layer upon layer. Do not whip or take the electrode out of the molten pool. Point the electrode slightly upward so that arc force helps control the puddle. Travel slow enough to maintain the shelf without spilling. Use currents in the lower portion of the range. The best thing to do is practice on some scrap pieces - and don't be discouraged if it seems like all the weld metal falls down & causes "grapes". It took me quite a while to figure out vertical up welding! Is there anyplace downhands can be used? Yes, I use them all the time for things like handrail work & seal welds. When we fab a handrail from, for example, 1-1/2 x 1-1/2 square tube, by the time the flat & overhead welds have been done at a connection that's already 3" of weld - way stronger than the tube itself. The two verticals get a quick downhand to close up the connection - strength isn't a factor here. And things like wood stoves & oil tanks have to be welded all around to seal them up - again downhands work well for this application. Generally, tanks & stoves are made of pretty light metal to begin with, so by the time they're tacked together that's about enough weld strength to hold the structure together. The rest of the welding is to ensure the assembly is air/water tight.