On the Rad City, a smaller diameter tube runs just an inch or two below the main rack. It's a shame they didn't do this on the RadWagon, the model that needs it most due to the rack tube diameter being too large to fit any off the shelf bag I've found. We're left with either modifying the bag, rack/frame, or both.

For the black pieces that actually mount to the fame, are those off the shelf parts or did you have those custom made?