I ship models all the time, to include large-scale helos, and all over the world. The best way to ship them is to get a box a few inches larger in each direction. Put a layer of packing peanuts on the bottom, then place the model in. Fill the rest of the voids with more packing peanuts. Slightly overfill the box so the peanuts are tight and the model is not allowed to move around. There may still be some minor breakage of small items. As long as you tell the buyer that small breakage can occur and you are not responsible for breakage, you should be good.
Don't go the newspaper and styrofoam block routes. They will allow too much movement and the model will break up. I found this out the hard way when I started shipping them many years ago. Since using the peanuts method, I have had almost none damaged.