1CharmShort -- you described what I think will go on, too. Thank you for explaining it perfectly!
There is no reason the flat mail rate shipping box can't be the tote. The idea is to keep it all together, right? A big ole zip lock bag to keep everything dry tucked into a flat rate box sounds reliable to me. But if I can create a tote just for this project, that might be fun, too.
We are supposed to send fabric with every round to help us keep the quilt tied together no matter what. Is a fat quarter of a key fabric you used big enough? A fat eighth won't make it through five rounds and anything bigger than a fat quarter seems like overkill. All the fabric may ultimately have to be used by the originator of the center or the pieces can be sewn together to make the back. I haven't made my center yet. Perhaps the center maker should send a half yard of key fabric(s)? I am thinking about the BOOM swaps and how extra fabric is really helpful in case of oopsies. Maybe Ricky will tell us how to plan this out.