Okay, so I removed the plywood subfloor on Sunday. I went back this morning to my welder to let him take another look now that all the frame is easily visible. Looks like we are probably going to replace the entire main frame rails instead of splicing new frame rails behind the axles. They also want to use 5 inch box steel tubing at 3/16 thickness. Ive read all the threads on the problem with rust on the interior surface where you do not have access to paint and the dilemma to seal the box tube...