i sent my rifle in when it needed repairs thru my local gun store. they boxed it, and shipped it for $35, they wrote out a repair tag and that was that. NEF shipped it to me when the repairs were complete. i did not have to worry about the details.
i would however not risk sending a frame thru the mail, or any carrier yourself. an interpetation of the law could get you behind bars, worse case scenario... at best a head ache if things go sour. i regularly use the US post office to send barrels, bullets, brass and other things... my PO is very friendly towards me and that helps, but i wouldnt send a frame.
use a carrier and follow the instuctions that Illion has, get shipping insurance for your firearm.
glenn