I say if you don't cut them through the floor pan and weld the pans 100% to the 2x3 you are just about wasting your time. I hang out sometimes in a professional chassis shop and just watch and b.s. with the welded there. They ALWAYS come up through the floor pans and weld them solid. I don't know what class it was for but one of the door slammer type cars that is required to have so much of the stock floor pan left in the car to qualify had tube style connectors put in it from back to front and they came up almost half way through the floor pans and were welded solid. For the structual welds they use tig with the appropriate steel filler but for thr pans to the connectors they use tig with sillicon bronze filler to keep from burning up the sheet metal.

Eric