A joint that is not clean and tight will end up having an ugly, weak weld. Let’s make a jig, an invaluable tool that holds two chunks of metal at right angles while allowing ample room to weld tacks in the corner.
Make sure the clamps are right and flip it over. Weld tacks at points 1, 2, 3, and 4. Tack weld a nice, hot tack at each of the points.
Try G-4 for about 1 second at each point. The tack welds don’t have to be gigantic, since they are just holding it together so you can remove the clamps and weld a bead. Re-trim the wire stick-out to 3/8” after each weld.