If your setup is not OS3.5 or OS3.9 based, you can try this:
http://aminet.net/package/disk/misc/diskimage Otherwise, this one might hit the spot:
http://aminet.net/package/disk/misc/diskimage_device-os3 In either way, you'll end up with i.e DF4 or DF5, whatever you want.
From personal experience, I used the older package. It uses mountlist for device definition; ADF loading/unloading is issued from CLI, but if you havie MUI installed, there's a nice utility with decent interface.
For the second part of post, IMHO that wont work since only recoverable RAM disks are reset-survivable (although under some circumstances, trackloaders might pose as problem here)
