Through many years of having completed models being shipped around the world, here is how I solved my problem.
Get a box that is 25% bigger than the model you are shipping. Take two inch thick styrofoam sheets and build a box frame cradle to support the bottom of the model. The model should rest with the wings, nose and tail section making contact only. Make the cradle deep enough where the gear, prop and any thing hanging on the model will not come in contact with anything. My rule of thumb is two to three inches clearance. Trim and carve where the model will rest on the styrofoam. Make the carved out areas about 1/8 to 1/4 inch larger than the surface of the model. Line these areas with felt or foam insulation. Place the model on the cradle.
Using more styrofoam blocks build another box frame cradle to fit over the top. Make it where the top and bottom when joined will the the height of the shipping box. Tape the top cradle to the bottom cradle, when completed. You want the model to fit snug when the top and bottom is joined. Again make sure there is plenty of clearance for the vertical tail. When completed you will have a box shaped four sided cradle with the model suspended in it. The wing tips, nose, and tail section will be sticking out exposed.
Now the fun part starts. Place the cradled model centered into the shipping box. Glue the bottom of the cradle to the bottom of the box. Make sure there is plenty of space for clearance on all four sides for the model. Using more styrofoam blocks you want to wedge the cradle into the box. This to help protect it in case the glue should let loose. Do not place any styrofoam blocks directly in front of or rear of the model. You want air space there only. If the box is dropped, you don't want the styrofoam being driven back against the exposed areas. Once the model is securely trapped into the box, close up and ship.
By using this method, I have not had any models damaged at all during shipping. Not even a pitot tube broken off.
Berny
Phormer Phantom Phixer
On the bench
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