I work for one of the above mentioned companies. I won't say which one, and I don't think it matters. Pack well. Expect the package to be dropped and thrown about. Forget "fragile" or "this side up" messages. The goal of package handlers is speed and speed alone. This doesn't mean we live without scruples or morals; it's just the nature of the biz. I believe both companies work hard at delivering packages accurately and timely. However, heed the above advice and pack well.
FYI: Those homemade plywood boxes are interesting and seem quite sturdy.
FYI: Those homemade plywood boxes are interesting and seem quite sturdy.