I have never worked with IR film so what I am sugessting is tentative. I believe that there are changing bags that are IR proof. If I am correct in that guess then why not get such a changing bag and ship your film cannisters inside the changing bag. It might also be extremely handy to have use of the bag during the trip...you may already own such a bag. I am not conjecturing that an IR proof bag will shield your film from gamma rays but I doubt that it could hurt.