I am in the process right now of replacing my entire floor pans and front two channel supports. I used the Harbor Freight spot weld bit. These took a little bit to get the hang of but once I figured it out it went really fast. Get a decent center punch, I used the Harbor Freight one and it is now dead, but it served its purpose.
I'd say for $5 a drill bit, they were well worth it. I haven't even flipped over to the other side yet.