I have not been involved with the "weld to floor" designed connectors. What I gather from the internet is that the weld to floor connectors are cut from channel and get seam welded to the floor. This is a less than desirable design. If the channels had flanges and could be plug welded to the floor with tight tolerance, I would be more inclined to consider that design as equal to or even superior to the square or rectangular tubing. I can see the existing "weld to floor" design tearing out or separating as Brooks James has witnessed. Just an old, burned out Body Man's opinion.
