I don’t see where the rule allows you to cut the rocker or any other part of the body open to add that bar. I could have had one less bend in my nascar bars (thus stronger) if I could have notched he door jamb but could not see where that was allowed.
Eric, I think Dick is right. Can you get the tube in the rocker without cutting anything? Probably not, but if you could, then I don't see anything prohibiting it either. The rules only allow gutting of the door and modifying the dash to put in the cage, nothing more.