I just don't see how this is meant to work, Bob has fixed dates all through July, August, all September off, and dates through October and November, so, if Mark was to be there, it would just be as a guest, not a proper double billing tour like he did with EmmyLou, maybe Bob is recording in September, and Mark will be involved in that, remember Mark has said in the past he tours around his kids schooling, so that would only give him August to join Bob on stage.