There was talk about this in another topic. Though I was thinking like you, frame mount is better, the predominant response was that the body mounts were actually better. A couple of guys stepped on their frame mounted steps with the body off of the frame and were surprised to see the amount of frame twist they create. Obviously, the twist will eventually lead to fatigue. Try finding that thread, it's no more than a couple of weeks old. It'll give you good advice, better than me.