With temps now into the low 60's, I'm back at it. I was able to get the first major butt joint to fit up well enough that it's pretty difficult to point out. Lots of grinding and sanding were needed, as well as some inverted welding; the steel is so thin that, when brought to a molten state to fuse the parts together, it yields to the pull of gravity and tends to sink. I end up turning the piece over and welding it upside down to counteract this effect - it's better to have a slightly high spot to grind down than a divot that needs punching back out. I was also able to get a pretty clean filet around the base, so it may not require any chasing. I find that these structurally critical areas are better left unground to avoid weakening the connection. This is turning out to be my most complicated assembly to date, but also a really fun challenge.