i've sold quite a few guns in the last few years, what i do is i remove the slide but leave the recoil spring and GR assembly as is in the slide. i wrap the slide alone in cling wrap , wrap the top of the frame so the inside isn't exposed to foreign matters, then put an empty mag inserted in...done and safe.
as for the package description it is not canada post business, so fragile tools or whatever comes to mind, and i'm asking the buyer to get extra insurance since it cost 2.50 dollards for each 100$ in extra .express with sig comes with a 100$ insurance, but in case of restricted sure enough i will never get a gun expedited to me without it being fully covered.