.....As Pat & Dave said Tig is the best way.... But if all you have is an arc welder & you don't want to pay someone to do it, you might try putting a back up piece inside the tubing. Example is if the tubing is 2 1/2" ID then put a piece of 2 1/2" OD {1/2" wide} inside to back up the weld. Run it hot & roll the pipe like Pat said so that your always welding in the flat position. Or put a piece of 2 1/2" ID on the outside if your using 2 1/2" OD tubing. Two lap joints might be easier for you to weld than 1 butt joint.... Or you might try rolling the tubing doing the welding all uphill or all downhill.... just a thought...... But again, as Pat & Dave said, Arc welding pipe/tubing is about as hard as it's going to get!!! Bill

ps, don't know what size rod your using but 3/32" rod is easier to control than 1/8".....