those blank images are pretty cool.  and you can use the import/export utilities

but yes pre made is kinda nice

http://www.bigmessowires.com/2015/02/13/rom-inator-disk-setup-tutorial/

start reading at " creating an image "  its the same concept.

Steve knows this stuff well, and he has a great way of explaining things, (simply), toboot!

here is a link to a pretty useful HD20 image as well.

this one