Do you not need a pulse type MIG. I TIG mine, but I have seen a MIG welded T45 cage, and the penatration looked terrible. The weld seemed to be sitting on top of the joint.
Inspected a T45 migged up cage last week. Installer used specific T45 wire and apart from 2 welds not welded circumferenially, was all good. Installer was a competent welder
before you play with the cage set up a couple of joints and practice on them, then set them up in a really awkward place and do it again. then do your cage.