I might try it , it’s definitely possible. I’ll have a think first . I could piece a ply disc in and loose the lashing points also but not to keen as it will likely show through the vinyl .Couldnt you trim the Caravelle rear threshold to clear the lashing points? Thats what I would do. the Caravelle trim is much better than the Kombi I had.
I have been looking to see if there is an aftermarket threshold that’s narrow like the kombi one but deep like the velle !