My picks would be a Pelikan case with fitted foam, or a Halliburton also with fitted foam. Either would be sturdy enough and both have good track records in that sort of application. However the airlines have managed to damage two of my Halliburton suitcases, FWIW.
Keep in mind that you cannot lock checked baggage any longer (you can, but it has to be a lock that TSA can open, if they can open it, anyone else who is equipped can too).
Instead of checking bags, I'd be inclined to ship the stuff between destinations with FedEx or perhaps UPS. With the baggage fees the airlines now charge, it might be cheaper even with overnight service. Take anything you must have immediately on arrival in carry-on, and ship the rest of it either to your hotel or a rep at the destination.
+1 on forget about putting sensitized materials in any checked bag, if they can't tell what's there they will open the bag and any "protective" containers, and they won't necessarily put everything back in the way you'd like.
My one experience with an x-ray bag for film was before the modern rules, and with a carry-on. The operators ran my bag through, then did it again, and then a few more times, each time with a long pause in the machine, then opened it for inspection. A colosal waste of everyone's time, especially mine. With all the suspicion and rules that exist now, I wouldn't remotely consider using one of those things.