Its realy easy but could be harder if you have a lots of guns! shipping will be expensive $$$ and yes guys its work!
Just take appart your gun in 2 or 3 parts, ex an AEG you will need 3 box, one with the upper receiver, the second with the lower receiver and gear box, the last one with accessories like the stock, mag, for-grip, silencer .....
if you have a GBB more simple, one box with the slide and mag, the second box with the lower handle.
On your box just whrite and Invoice just whrite: Accessories Toys Parts
AND YES ITS WORK i from Quebec City and i order my gun from REDWOLFAIRSOFT and sometime i buy them used from particular in USA and i always receive my guns with all parts
just bought a Classic Army SCAR CQC with for-grip and Silencer 3 weeks ago on ebay from a private in USA i asked him to take appart the gun and to ship it in 3 separated boxs, i receive my gun in 3 days from Maryland USA
and ive bought 2 GBB a WA 1911 and a Tanaka Sig Sauer From REDWOLFAIRSOFT with the same procedure and ive recived them a week later with out problem!