I've thought about mine a bit since install and have come up with a plan for next time (???).
Start out with an 1/8" plate, 6"X6", and radius each corner to 1/2" round and drill appropriate holes for mounting bolts. Also relieve the sharp edge all the way around the lower edges of the plate with a grinder. Clean up with a flat file.
Then take another 1/8" plate, 4"X4", and after radiusing the corners, sandwich it on top of the larger plate at a 45° diagonal. Weld the tube to this assembly and add a couple of small gussets to increase weld area.
This creates a base plate that is strong (1/4" thick), but gives a little around the perimeter and will lessen the chance of cutting through the floor panel. A further enhancement would be to change the 6"x6" plate to 6"X8" and bend a 2", 90° flap to butt against the rocker panel channel section (with additional fasteners).
My current B hoop ties into rock rails underneath. Any future build would have 1/8" plate brackets underneath angling to the frame rail. These could be attachment points for rock rails as well.
I prefer bolting to and thru the floor vs welding. I think the welded area adjacent to the plate would be prone to failure.