TIG on steel seems to be a lot easier than aluminum. My lone experience with TIG on aluminum was almost disastrous. Let's just say molten aluminum was leaving the part faster than I could add it.
+ TIG with capability to weld 1/4" steel is $$$, not to mention electrical service rated to drive that box. I bought a TIG machine after a MIG, and I seriously doubt I would have been happy with TIG only for 4+ years.