On dragging 6011 I don't think you'll be able to or like the results. One is the fact that you're running a AC machine. My experience with my old buzz box is that 6011 won't drag with it unless the current is set way to high for the thickness of metal that you're welding (it's possible on really thick stuff and high amperages but still not recommended). Now I can drag it some with my stiffer high powered DC industrial machines but it produces a high narrow bead that's not wanted (the only exception I've seen is that the root pass on pipeline work around here is done that way).
You should be watching the trailing edge of the weld pool primarily with secondary attention to the leading edge (just to make sure it's actually melting into the metal on both sides). The trailing edge tells the most info of how the welds going. If it's melting into both sides you'll see the molten metal drawing itself into the work in. If it's building up to much you can see it in the trailing edge. If there's not enough build up you can see it there as well. In other words you can tell most of what you need to know by watching the trailing edge. Did I say that enough times. :-)
It can be difficult to weld with a high slag rod on a deep groove provided by a round object sitting on a flat object. It's not impossible but it does take practice and personally I've never liked
6013 for that particular reason.
My advise here is to butt the corner joints corner to corner leaving a nice 90 V for the weld to fill. In this case properly run 6013 will give a nice smooth round cornered appearance to the box. Though my preference is still for 7018 for jobs like this.
I like 7018 for it's smooth weld with less slag than 6013 making it easier for me to run. However it's a DC only rod unless you buy the kind specifically made for AC. As for the purist cry that it's has to be kept in a oven all I can say is that there's many many pounds of it run all the time that's not been oven kept. If it's a critical job then yes it should be kept in a oven. But for mild steel as long as it's kept reasonably dry then it's perfectly possible to make acceptable welds with it.
Wayne Cook Shamrock, TX