I am in no way asking you to hold it for me but I ordered my Corbin 2 weeks ago and still waiting to get it as they had to make it. I also just installed Phil's Rack with the GIVI E55 so I would want to make sure that the backrest would still fit on the Corbin with the topcase installed as I think it would be a softer backrest than the GIVI topcase backrest.
Just saying once I get my seat, if it is still available, I would be interested if it looks like it would still fit with the case otherwise, best of luck with your sale.