About this ram (hard) disk, should it be set as read-only? Are you adding specific CHS values too (to memdisk)?
Additionally, why we would need to use a different drive letter? I think the ram (hard disk) drive should preserve the ram drive letter as used by fdubcd.ISO, so additional letters can be used for additional drives (like additional optical drives for example, which is the situation we are discussing in this topic). And leaving a drive letter free for a ram floppy disk (as was used until now, fdubcd.img of 2880kb) might still be useful in some situations.
Additionally, why we would need to use a different drive letter? I think the ram (hard disk) drive should preserve the ram drive letter as used by fdubcd.ISO, so additional letters can be used for additional drives (like additional optical drives for example, which is the situation we are discussing in this topic). And leaving a drive letter free for a ram floppy disk (as was used until now, fdubcd.img of 2880kb) might still be useful in some situations.