Definetely do more than peaunuts. I would try an build a small wooden crate that goes inside of a cardboard box actually, and inside the crate I would put some of styrofoam that fits the sub, and fill in the loose areas with peanuts.
but put the sub in a plastic bag too, so nothing gets inside the sexiness.
if u can get all that done, try and get some strong cardboard edges, that go on the box, for more support.
Tape the thing up, write "HEAVY" and "FRAGILE" on it. Or at least heavy, possibly "MAGNETIC" or something.
I work at fed ex, so im just giving you advice on how to not piss off the package handlers, so they handle the heavy box nicely.
Packing a box poorly only adds to the abuse it will recieve. Not conciously, but it just sort of happens.