Then the ups golf club box is perfect size, buy direct at any ups store.
Wal-Mart for bubble wrap, cling film, peanuts, maybe packing paper too.
I have shipped many speakers I sold here and eBay using same method.
Last ones were b&w 804d.
All arrived safely.
I wrap the speaker first then slide into the box or slide box over the speaker. Lots of packing once in the box to stop it moving around.
You have to make it so the only way they could damage it would be to run over it!
Also lots of fragile and handle with care signs on box too.
Not sure if they take notice but in event of damage it helps your cause on any claim!