The problem with A36 or mild steel pipe is that it has a seam that can split under load if not oriented correctly where as tubing doesn't have the seam and because it's mandrel drawn it is in a restively neutral stress state, where as mild steel tubeing is rolled from flat stock and seam welded, tubing will cut, grind and weld quite easily, MIG and TIG work really well but stick can be used if the welder is good enough and has a machine that will handle lower amperage at a constant rate, most home boxes won't but a home MIG will, a TIG machine is the best but usually the cost of one precludes a home owner owning one not to mention the skill it takes to operate one.
All I can say is that if it was me doing this I would use tubing and MiG it.
That's why some of those things cost so much...expensive materials and done by pro's.... So I don't have to worry... Being a retired shop teacher I have seen all sorts of Farm Engineering... some quite good.. some interesting... and some just flat out dangerous.... I trust my welding skills to things that can't cause me to crash and burn.
Joel
