I shipped 2 SS X-wings, one to UK and one USA and both arrived intact, took me a good 2 hours to pack properly, if the cannons are just glued no pins they will most probably come unglued with small impact.
Basically the model has to be floating in the middle of the box, I first bubble or foam wrap fuselage and wings, then add big foam rings around fuselage to stabilize and keep the whole ship in a suspended position so the wings don't touch anywhere, I add foam on front tip and rear engines, basically you have to build a foam frame around ship and fill up with foam peanuts, would be a ton easier if the wings came off.
GFollano