Re: DOM vs ERW for roll cage.
A flux cored (FCAW) is way less likely to pass tech than a proper gas shielded MIG weld. WAY less: look for probable future rule wording that states that cage welds must be MIG or TIG, no stick, no flux core.. We are seeing simply horrible welds.
Just sayin......
I would tend to think MIG, then Stick/Arc welds would be the most preferable methods in doing cage work. Flux simply doesn't do it when it comes to penetration. Yes, it is possible, but it's like using duct tape instead of a nut and bolt. TIG may be the prettiest, but like rob said, it's slow and I'd imagine difficult to do properly in tight clearances and while inverted. I'd take a sloppy but sturdy Stick/Arc cage over just about anything except a properly done MIG cage any day of the week. The point is tight fits, and good penetration.