I have a case I picked up at Fleet/Farm (those in the Midwest will know) that is made out of the same steel that pickup tool boxes are made from. It holds the Mauser dad brought home from Germany.
It certainly must have been discrete enough - the mover, when we moved from CA to WA saw it in the garage, simply picked it up and put it on his truck before I could tell him not to (it's not legal for him to transfer a firearm, even cased, anywhere, let alone across state lines).
I let him take the chance - when he showed up at the other end, and unloaded, since we had about 3 other guitars, he asked if it was an "ax" in the case. I didn't want to burst his bubble, he probably still is telling the story about the "really valuable guitar in the special locked case" that he moved! [shock]
I think that would be much more discrete than those on the Eagle site - even though they were nice cases.