A 140 will do fine on a pickup frame. However, I agree that a frame isn't something to learn to weld on. You need to practice with a lot of scrap like I did 50 years ago. I still use scrap of similar thickness to get my setting on if its a machine I don't use every day. Welding on the web of a frame is not that critical. The flanges are where your strength is.
Speaking of Hobart 140's, just last weekend I welded a 3/8 chain clevis on to my loader bucket to pull fence posts with. The weld looks just as good as if I had done it with my Millermatic 200.
