After high school I worked for a moving company for for about 8 months, and what they'd do for overseas moves (including cars!) was to pack everything into huge wooden crates. Now I have zero idea if they go through every single little thing in those huges crates, I'd suspect it that they wouldn't, and would probably just check the contents of the occasional crate based upon what the manifest was labelled as.
One thing you might want to do is completely disassemble your airsoft guns, list them as paintball guns, pack ammo elsewhere (as mentioned above) and put a few bags of 6mm paintballs (if you can find) in with your disassembled guns. At least if the box containing the airsoft parts gets opened, they are pretty obvious that they are not real guns. Still, it's a risk, and one I'm sure I wouldn't want to try myself.