skip the box, buy some pvc pipe and a couple pvc caps...
stuff some junk (paper, foam, whatever) down the sides of the barrel in the pvc pipe, and stuff the caps with stiff foam (or whatever works). Compress the shit out of it, and tape it up real tight. slap a sticky shipping label on the pvc tube, and I bet that thing would make it around the world a couple of times without getting beat up.
That's the ONLY method I've used that didn't result in a flippin mess on the receiving end.
I've received chewed up barrels (due to insufficient packaging), and I've sent perfect barrels in what I though was 'good enough' packaging that ended up trashed. If you want to avoid situations like that, the pvc pipe method is the ONLY way to go