I'm trying again by sending some to Brazil. The receiving member is also donating some seeds in return, hopefully both letters make it through.
That being said, I have only attempted letter sized mailings due to cost (under $2 US) vs a minimum of around $15 for a package.
A small box might be the next attempt, but the recipient of that test would have to pay for half of that cost. Maybe they get six months worth of requests to make it worthwhile.
We'll cross that bridge we get there.