Mine are not welded to the floor at all, just front and back. I probably wouldn't go to all that trouble again, but I already had the material. I would just buy the 3X1.5 tubing and avoid the clearance issue. I couldn't bring myself to cut up the virgin floors, so I cut the connectors instead.
Here is my favorite action pic from my last trip to the track, for the person who asked. (I think the frame connectors are working)
