I need some suggestions as to how to ensure the blocks will surive multiple mailings, .......... wouldn't you just lay them flat in a box, packed tight?
and also what to use to mark the signature area on the blocks that won't fade for 3-4 weeks! ............... the Pilot Frixion pens will not disappear until they are rubbed (friction/frixion) or the hot iron does the vanishing act. Plus they make a very nice fine line.
Starch the fabric up well, before cutting, and you'll have very minimal fraying. First check on a sample piece that the markers they will be using for their names work fine on the starched fabric. Likewise for your edge marker and when pressing after. I'm sure there'll be no problems, but better to check now, than later discover a problem.