I've been evolving my process for shipping minis since I first started dealing in used expansions early in the Fall of 2015. I started with what I thought worked, and based on feedback (and the subsequent refunds) began to change my process to make shipping more and more secure. Now as I write this, it's been several months since I've received a complaint on a mini arriving broken.
To start with, let's lay out the supplies we're going to using:
Shipping Box Any properly sized box will do. For shipping 1-4 small expansions I like to use the USPS small Flat Rate Shipping boxes. You can pick these up for free at your local Post Office, or you can order them in bulk from USPS.com.
Packing Tape The enemy of fragile models is movement. No models ever broke just sitting on a shelf without anything moving it. Stopping movement requires tape. I buy mine in bulk from Amazon.
Packing Peanuts X-Wings, Z-95s, and B-Wings have delicate protruding gun tips. TIE Fighters of all kinds have panels. StarVipers have a delicate curve to them. All of these things can undergo torque during shipping and break. To prevent that we need to use something to hold them still. Single packing peanuts are fantastic for this. I get mine when shipments come in from other places. Find some and keep a stash.
Small Bubble Wrap or Foam To properly pack the models we need to surround them in something cushiony and stable. I use the bubble wrap or foam that comes on other things I buy online. You'd be surprised how much shows up at your door with bubble wrap in it.
Securing the Models
Now that our supplies are lined up, let's get to packing the models. There are a few different categories of models, and each one requires a different packing method.
Flat Models The easiest to pack are the flat models. A-Wings and Y-Wings fall into this category. Simply cut enough bubble wrap of foam to surround the model, roll it up, and tape it shut. Make sure you tape both of the ends closed as well.
Large ships fall into the flat ship shipping category as well. Even ones that aren't exactly flat, like the Firespray-31, are sturdy enough to roll up securely in bubble wrap without additional protection.
PROTIP The width of two inch tape is long enough to be your length in many situations. I will often peel off about a half inch (1 cm) 'length' of tape and turn it sideways to use it. If you need longer than 2" you can stick more than one together.
Pointy Models X-Wings, B-Wings, and Z-95s all come with pokey pointy bits that are prone to snap off during shipping. This is the first place the packing peanuts will come in handy. In the case of X-wings and Z-95s you're going to poke the nose of the ship and the guns themselves through the packing peanut. This will hold everything steady during shipping, and prevent your wrapping from putting pressure on the pointy bits.
TIE Phantoms, TIE Interceptors, and TIE Defenders fall into the pointy model group as well.
B-Wings suck. These are the most difficult things to ship in X-Wing. No one ever does it right. Depending on the size of your packing peanuts, shipping a B-Wing is going to require at least two, but more probably three of them. You're still poking the guns through the peanut, but you have to use the peanuts pressing up against themselves to prevent the guns from snapping.
PROTIP Sometimes tape does not adhere to the foam well. If that's the case with you, use a long enough section of tape so that it wraps all the way around the model and adheres to itself. Closing off the ends can then adhere to the original tape.
Ships with Panels TIE Fighters and StarVipers fall into this category. These are similar to the pointy ships in that they have delicate parts that can succumb to torque during shipping, and ruin your customer's day when their models show up broken. To properly packing a TIE Fighter, use two packing peanuts, one on top and one on bottom to prevent the panels from flexing and snapping the struts.
Getting the packing peanuts just right is an exercise in Goldilocksianism. If you don't use a packing peanut large enough you won't prevent the strut from flexing, but if you jam a couple that are too large in there their pressure will pop the panel off for you. I will often choose peanuts that are slightly too large, and then cut them down a bit so that the fit is just right.
PROTIP Roll the TIE with the panels facing outward. This will keep the peanuts from falling out while you're trying to pack it.
With the model packed securely, everything else is a breeze.
Pilot Cards: Use standard 2.5"x3.5" card sleeves to store them. You can put about 10 pilot cards in a single sleeve.
Upgrade Cards: Use the mini-American card sleeves to pack these. You can fit about 8 cards in one comfortably.
Other Bits: The rest of the expansion (bases, pilot tokens, pegs, movement dials, etc) go into a Ziploc bag. Roll that bag up tightly, and secure it with your packing tape.
Packing the Expansion
Now that we have everything loaded in its carrying case it's time to put it in the box.
Sleeved cards get taped to inside lid of the box.
Everything else gets laid out however you can make it fit on the bottom of the box. As you lay things out use a piece of tape on each side to secure it to the box itself.
With everything in the box secure, simply fold the box up and seal it. You're now ready to ship.
And that's it. You're ready to ship. I'm always interested in improving my methods, so if you have an idea to make things better or more efficient, please feel free to share.