When I added a king tour pack to my bike, I never liked the open space beneath the passenger backrest where the speaker pods are located. Decided to pick up a pair of speaker pods, have them recovered to match the Corbin backrest pad and install. While I do not have any intention of putting speakers in these pods, the option exists as well as the possibility of using these to store "nick nacks" if some clever person on this site comes up with a speaker shaped glove box door (pj57 are you reading this?)!
Since I also have the George Anderson tour pack relocator, I wanted to fill in the gap between the tour pack and passenger pillion. My tour pack is moved back 2.5"' so I designed a pad shape that would fill in the space and also act as a lower lumbar support for my BSR and had it covered in the same material as the backrest and pods. Came out real nice and my wife says it's perfect for her lower back support.