Although a Classic I imagine my solution applies to CX with luggage rack as well. We use
's humungous suitcase wrapped in plastic bag and secured by the leather straps I got FOC with new car, which fit through dedicated slots in rack. The case is further secured laterally by lockable securing strap. I have a home made LED strip mounted on length of wood to act as brake light repeater. This tucks under leather straps and plugs into cobra feed. The SSL dual rate rear suspension copes admirably with the extra 20+Kg even with full tank although I add a couple of clicks to dampers.
Touring by myself, although often with dog, I use the period leather suitcase that I also got FOC. This simply because I have it, it looks great, has waterproof cover and enough space for my personal needs, the weight being suffered. The dog doesn't travel light but I have parcel shelf and footwell to accommodate his needs
