Howdy, I am needing to join (weld) a vertical member of square tubing to a
horizontal member that sits on the floor (all tubing being 2.5" x 3/16").

The problem, as you have likely come across, is that the corner of the
square tubing has a radius, leaving a gap on either end of the piece to be
joined.

How would you tackle this problem?

I can think of using a sharpie and an angle grinder to get it pretty close.
Is this about the best method?

Thanks for any suggestions,

Jon