I built 2 dom steel cages 15 years ago for a guy, welding method wasn't specified in their rule book, the only method I knew back then, was Stick welding with root and cap, the mig I had back then wasn't beefy enough.. I did a gapped fit up with a 6010 root, and then a 7018 cover pass.
The guy ended up hitting a large tree with one of the cars at high speed in passenger side frontal impact. None of the welds gave, the tubing bent and the frame rail sections ripped out of the unibody in places. The driver and navigator walked away from the crash. Weld porosity is a big problem
with stick welding, done wrong, its weak, done right, really strong. We use it a lot in plant construction, but we also have to do 10% xray on joints.
Porosity is pretty much non existent with tig, but can have shallow penetration and be a very pretty, but weak weld. Easy to undercut the joint with too.
When I do my cage for my next track car, I'm probably going to do a tig root and Mig cover pass. I don't build cages for people anymore with all the liability stuff...