7018 low hydro rods is what you want to use to get the penetration you want. I use to weld and built several feed lots and working pens and thats all we used. I remeber 1 cold day we tacked up about 300ft of rods using 6011s (2 7/8 post and top rail, 4 rods across) to weld the next morning, when we got there in the morning all the rods were on the ground

had to start all over