Nathan, I hope your ‘ribbing’ comment wasn’t directed at me. My comment was meant to illustrate the issue may not be as simple as the rule book may suggest, but the tech guys handle construction issues well case by case.
Anyway, I’ve looked at a quiet a few cars lately with tubular gussets and it looks like the consensus is a minimum of 1”x.120 tubing and I think dimensions should be 4” per side minimum. Similar to plate dimensions. If such a configuration was deemed inappropriate for a particular car due to adjacent tubing sizes/shape, or other craftsmanship issues plates can be added to either side (to close the triangle) to add additional strength.
I have limited experience with door cars, my focus is special construction. I can submit for rule change if this makes sense.
Josh