Meh. It's not like it's nitro. If you're feeling nervous, get some smaller cardboard boxes, and pack them in, so they're all pointing in the same direction, nice and tight; add a layer of corrugated, repeat. If not, just put them in boxes, shake the boxes to settle them, and pack with bubble wrap, or whatever, so they don't rattle around too much.
It may cost a few bucks more to ship two cartons as opposed to one, but package handlers are less likely to drop a lighter (though not light) carton. Depending on the type of ammo, 3,000 rounds is heavy, or heavier.
Invest in fiberglass tape, and go King Tut on the actual ammo containers. Put them in an overcarton, and use the tape, again.
Ship ground, make sure it has the proper black/white diamond label. Pay for insurance, if you like.
Don't think that not marking it will work - they'll know. If you ship it from a FedEx or UPS hub, get the tracking, and keep an eye on it.
I'll PM you my address, and let you know when it gets here - Thanks!