Slow your wire speed down, make sure your material is clean and weld away, you should do some pratice on some scrap before you go at it on your rig, if your gonna' do it anyway, stich weld the body, make a tack go about 4 inches or so away from that spot and tack again as to not heat and warp the metal and keep goin' when you have reached the end start over and soon you will be done remember to be patient dont rush it or the truck will look like
patience is a virtue these are not critical spots to weld but you should pratice first, most anyone can do it it just takes time and pratice.
GOOD LUCK